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  • DP练习（概率，树状，状压）

    http://vjudge.net/contest/view.action?cid=51211#overview

    花了好长时间了，终于把这个专题做了绝大部分了

    A：HDU 3853

    最简单的概率DP求期望，从终点推到起点就是了，注意一个坑就是如果p1=1那么他一旦到达这个点，那么就永远走不出去了

    题解

     1 //#pragma comment(linker,"/STACK:102400000,102400000")
 2 #include <map>
 3 #include <set>
 4 #include <stack>
 5 #include <queue>
 6 #include <cmath>
 7 #include <ctime>
 8 #include <vector>
 9 #include <cstdio>
10 #include <cctype>
11 #include <cstring>
12 #include <cstdlib>
13 #include <iostream>
14 #include <algorithm>
15 using namespace std;
16 #define INF 1e9
17 #define inf (-((LL)1<<40))
18 #define lson k<<1, L, mid
19 #define rson k<<1|1, mid+1, R
20 #define mem0(a) memset(a,0,sizeof(a))
21 #define mem1(a) memset(a,-1,sizeof(a))
22 #define mem(a, b) memset(a, b, sizeof(a))
23 #define FOPENIN(IN) freopen(IN, "r", stdin)
24 #define FOPENOUT(OUT) freopen(OUT, "w", stdout)
25 
26 //typedef __int64 LL;
27 //typedef long long LL;
28 const int MAXN = 1005;
29 const int MAXM = 100005;
30 const double eps = 1e-13;
31 //const LL MOD = 1000000007;
32 
33 double p1[MAXN][MAXN], p2[MAXN][MAXN], p3[MAXN][MAXN], dp[MAXN][MAXN];
34 
35 int main()
36 {
37     int R, C;
38     while(~scanf("%d %d", &R, &C))
39     {
40         for(int i=1;i<=R;i++)
41             for(int j=1;j<=C;j++)
42                 scanf("%lf%lf%lf", &p1[i][j], &p2[i][j], &p3[i][j]);
43         mem0(dp);
44         for(int i=R;i>=1;i--)
45             for(int j=C;j>=1;j--)
46             {
47                 if(i==R && j==C) continue;
48                 if(fabs(p1[i][j] - 1) < eps) continue;
49                 dp[i][j] = (dp[i][j+1]*p2[i][j] + dp[i+1][j]*p3[i][j] + 2) / (1-p1[i][j]) ;
50             }
51         printf("%.3lf
", dp[1][1]);
52     }
53     return 0;
54 }
    View Code

    B:HDU 3920

    状态压缩DP  题解

      1 //#pragma comment(linker,"/STACK:102400000,102400000")
  2 #include <map>
  3 #include <set>
  4 #include <stack>
  5 #include <queue>
  6 #include <cmath>
  7 #include <ctime>
  8 #include <vector>
  9 #include <cstdio>
 10 #include <cctype>
 11 #include <cstring>
 12 #include <cstdlib>
 13 #include <iostream>
 14 #include <algorithm>
 15 using namespace std;
 16 #define INF 1e9
 17 #define inf (-((LL)1<<40))
 18 #define lson k<<1, L, mid
 19 #define rson k<<1|1, mid+1, R
 20 #define mem0(a) memset(a,0,sizeof(a))
 21 #define mem1(a) memset(a,-1,sizeof(a))
 22 #define mem(a, b) memset(a, b, sizeof(a))
 23 #define FOPENIN(IN) freopen(IN, "r", stdin)
 24 #define FOPENOUT(OUT) freopen(OUT, "w", stdout)
 25 template<class T> T CMP_MIN(T a, T b) { return a < b; }
 26 template<class T> T CMP_MAX(T a, T b) { return a > b; }
 27 template<class T> T MAX(T a, T b) { return a > b ? a : b; }
 28 template<class T> T MIN(T a, T b) { return a < b ? a : b; }
 29 template<class T> T GCD(T a, T b) { return b ? GCD(b, a%b) : a; }
 30 template<class T> T LCM(T a, T b) { return a / GCD(a,b) * b;    }
 31 
 32 //typedef __int64 LL;
 33 //typedef long long LL;
 34 const int MAXN = 105;
 35 const int MAXM = 100005;
 36 const double eps = 1e-13;
 37 //const LL MOD = 1000000007;
 38 
 39 int T, N;
 40 typedef double Point[2];
 41 Point st, p[MAXN];
 42 double dis[MAXN][MAXN], d[MAXN], dp[1<<21];
 43 
 44 double calc(Point a, Point b)
 45 {
 46     double x = a[0] - b[0];
 47     double y = a[1] - b[1];
 48     return sqrt(x*x + y*y);
 49 }
 50 
 51 void getDis()
 52 {
 53     for(int i=0;i<N;i++)
 54     {
 55         d[i] = calc(st, p[i]);
 56         for(int j=i+1;j<N;j++)
 57         {
 58             dis[j][i] = dis[i][j] = calc(p[i], p[j]);
 59         }
 60     }
 61 }
 62 
 63 int main()
 64 {
 65     int t = 0;
 66     scanf("%d", &T);
 67     while(T--)
 68     {
 69         scanf("%lf %lf", &st[0], &st[1]);
 70         scanf("%d", &N);
 71         N <<= 1;
 72         for(int i=0;i<N;i++)
 73             scanf("%lf %lf", &p[i][0], &p[i][1]);
 74         getDis();
 75         dp[0] = 0;
 76         for(int i=1;i<(1<<N);i++) dp[i] = INF;
 77         queue<int>q;
 78         q.push(0);
 79         while(!q.empty())
 80         {
 81             int now = q.front(); q.pop();
 82             int f=0, r;
 83             while( now & (1<<f)  && f < N)
 84                 f++;
 85             for(r = f + 1; r < N; r ++ )
 86                 if(!(now & (1<<r)))
 87             {
 88                 int next = now | (1<<f) | (1<<r);
 89                 double minDis = MIN(d[f], d[r]) + dis[f][r];
 90                 if( fabs(dp[next] - INF) < eps )
 91                 {
 92                     q.push(next);
 93                     dp[next] = dp[now] + minDis;
 94                 }
 95                 else if( dp[now] + minDis < dp[next] )
 96                     dp[next] = dp[now] + minDis;
 97             }
 98         }
 99         printf("Case #%d: %.2lf%
", ++t, dp[(1<<N)-1]);
100     }
101     return 0;
102 }
    View Code

    C:HDU 1520

    简单的树形DP  题解

     1 //#pragma comment(linker,"/STACK:102400000,102400000")
 2 #include <map>
 3 #include <set>
 4 #include <stack>
 5 #include <queue>
 6 #include <cmath>
 7 #include <ctime>
 8 #include <vector>
 9 #include <cstdio>
10 #include <cctype>
11 #include <cstring>
12 #include <cstdlib>
13 #include <iostream>
14 #include <algorithm>
15 using namespace std;
16 #define INF 1e9
17 #define inf (-((LL)1<<40))
18 #define lson k<<1, L, mid
19 #define rson k<<1|1, mid+1, R
20 #define mem0(a) memset(a,0,sizeof(a))
21 #define mem1(a) memset(a,-1,sizeof(a))
22 #define mem(a, b) memset(a, b, sizeof(a))
23 #define FOPENIN(IN) freopen(IN, "r", stdin)
24 #define FOPENOUT(OUT) freopen(OUT, "w", stdout)
25 template<class T> T CMP_MIN(T a, T b) { return a < b; }
26 template<class T> T CMP_MAX(T a, T b) { return a > b; }
27 template<class T> T MAX(T a, T b) { return a > b ? a : b; }
28 template<class T> T MIN(T a, T b) { return a < b ? a : b; }
29 template<class T> T GCD(T a, T b) { return b ? GCD(b, a%b) : a; }
30 template<class T> T LCM(T a, T b) { return a / GCD(a,b) * b;    }
31 
32 //typedef __int64 LL;
33 //typedef long long LL;
34 const int MAXN = 6010;
35 const int MAXM = 100005;
36 const double eps = 1e-13;
37 //const LL MOD = 1000000007;
38 
39 int N, a[MAXN], dp[MAXN][2];
40 int fa[MAXN];
41 vector<int>e[MAXN];
42 
43 void DFS(int u)
44 {
45     int s0 = 0, s1 = 0;
46     for(int i=0;i<e[u].size();i++)
47     {
48         DFS(e[u][i]);
49         s0 += MAX( dp[e[u][i]][0], dp[e[u][i]][1] );
50         s1 += dp[e[u][i]][0];
51     }
52     dp[u][0] = s0;
53     dp[u][1] = s1 + a[u];
54 }
55 
56 int main()
57 {
58     //FOPENIN("in.txt");
59     while(~scanf("%d", &N))
60     {
61         mem0(dp);
62         for(int i=1;i<=N;i++)
63         {
64             scanf("%d", &a[i]);
65             fa[i] = i;
66             e[i].clear();
67         }
68         int x, y;
69         while(scanf("%d %d", &x, &y) && (x||y) ){
70             e[y].push_back(x);
71             fa[x] = y;
72         }
73         int ans = 0;
74         for(int i=1;i<=N;i++) if(fa[i] == i)
75         {
76             DFS(i);
77             ans += MAX(dp[i][0], dp[i][1]);
78         }
79         printf("%d
", ans);
80     }
81     return 0;
82 }
    View Code

    D:HDU 4284

    状态压缩DP  题解

      1 //#pragma comment(linker,"/STACK:102400000,102400000")
  2 #include <map>
  3 #include <set>
  4 #include <stack>
  5 #include <queue>
  6 #include <cmath>
  7 #include <ctime>
  8 #include <vector>
  9 #include <cstdio>
 10 #include <cctype>
 11 #include <cstring>
 12 #include <cstdlib>
 13 #include <iostream>
 14 #include <algorithm>
 15 using namespace std;
 16 #define INF 1e8
 17 #define inf (-((LL)1<<40))
 18 #define lson k<<1, L, mid
 19 #define rson k<<1|1, mid+1, R
 20 #define mem0(a) memset(a,0,sizeof(a))
 21 #define mem1(a) memset(a,-1,sizeof(a))
 22 #define mem(a, b) memset(a, b, sizeof(a))
 23 #define FOPENIN(IN) freopen(IN, "r", stdin)
 24 #define FOPENOUT(OUT) freopen(OUT, "w", stdout)
 25 template<class T> T CMP_MIN(T a, T b) { return a < b; }
 26 template<class T> T CMP_MAX(T a, T b) { return a > b; }
 27 template<class T> T MAX(T a, T b) { return a > b ? a : b; }
 28 template<class T> T MIN(T a, T b) { return a < b ? a : b; }
 29 template<class T> T GCD(T a, T b) { return b ? GCD(b, a%b) : a; }
 30 template<class T> T LCM(T a, T b) { return a / GCD(a,b) * b;    }
 31 
 32 //typedef __int64 LL;
 33 //typedef long long LL;
 34 const int MAXN = 600;
 35 const int MAXM = 100005;
 36 const double eps = 1e-13;
 37 //const LL MOD = 1000000007;
 38 
 39 int T, N, M, H, Money;
 40 int dis[MAXN][MAXN], add[MAXN], cost[MAXN];
 41 int citys[20], dp[1<<18][18];
 42 
 43 void init()
 44 {
 45     int u, v, w, c, a;
 46      mem0(add); mem0(cost);mem1(dp);
 47     scanf("%d %d %d", &N, &M, &Money);
 48     for(int i =0 ; i <= N ;i ++ )
 49     {
 50         dis[i][i] = 0;
 51         for(int j = 0; j <= N ; j ++ )
 52             if(i != j) dis[i][j] = INF;
 53     }
 54     for(int i = 0; i < M; i ++ )
 55     {
 56         scanf("%d %d %d", &u, &v, &w);
 57         dis[u][v] = dis[v][u] = MIN(dis[u][v], w);
 58     }
 59     scanf("%d", &H);
 60     for(int i = 1; i <= H; i ++ )
 61     {
 62         scanf("%d %d %d", &u, &a, &c);
 63         citys[i] = u;
 64         add[i] = a;
 65         cost[i] = c;
 66     }
 67 }
 68 
 69 void floyd()
 70 {
 71     for(int k=1;k<=N;k++)
 72     for(int i=1;i<=N;i++)
 73     for(int j=1;j<=N;j++)
 74     {
 75         dis[i][j] = MIN(dis[i][j], dis[i][k] + dis[k][j]);
 76     }
 77 }
 78 
 79 int main()
 80 {
 81     //FOPENIN("in.txt");
 82     while(~scanf("%d", &T)) while(T--)
 83     {
 84         init();
 85         floyd();
 86         int ans = -INF; H += 1;
 87         citys[0] = 1; cost[0] = add[0] = 0;
 88         dp[1][0] = Money;
 89         for(int now = 1; now < (1<<H); now ++ )
 90         {
 91             for(int u = 0; u < H; u ++ ) if(dp[now][u] != -1)
 92             {
 93                 for(int v = 1; v < H; v ++ ) if( (now & (1<<v)) == 0 )
 94                 {
 95                     int next = now | (1<<v);
 96                     if(dp[now][u] >= dis[citys[u]][citys[v]] + cost[v] )
 97                     {
 98                         dp[next][v] = MAX(dp[now | (1<<v)][v], dp[now][u] - dis[citys[u]][citys[v]] - cost[v] + add[v]);
 99                     }
100                     if(next == (1<<H) - 1)
101                     {
102                         ans = MAX(ans, dp[next][v]);
103                     }
104                 }
105             }
106         }
107        //printf("%d
", ans);
108         printf("%s
", ans >= 0 ? "YES" : "NO");
109     }
110     return 0;
111 }
    View Code

    E:HDU 2196

    比较好的题目了，两次DFS，求树上任意点触发的最长距离 题解

     1 //#pragma comment(linker,"/STACK:102400000,102400000")
 2 #include <map>
 3 #include <set>
 4 #include <stack>
 5 #include <queue>
 6 #include <cmath>
 7 #include <ctime>
 8 #include <vector>
 9 #include <cstdio>
10 #include <cctype>
11 #include <cstring>
12 #include <cstdlib>
13 #include <iostream>
14 #include <algorithm>
15 using namespace std;
16 #define INF 1e8
17 #define inf (-((LL)1<<40))
18 #define lson k<<1, L, mid
19 #define rson k<<1|1, mid+1, R
20 #define mem0(a) memset(a,0,sizeof(a))
21 #define mem1(a) memset(a,-1,sizeof(a))
22 #define mem(a, b) memset(a, b, sizeof(a))
23 #define FOPENIN(IN) freopen(IN, "r", stdin)
24 #define FOPENOUT(OUT) freopen(OUT, "w", stdout)
25 template<class T> T CMP_MIN(T a, T b) { return a < b; }
26 template<class T> T CMP_MAX(T a, T b) { return a > b; }
27 template<class T> T MAX(T a, T b) { return a > b ? a : b; }
28 template<class T> T MIN(T a, T b) { return a < b ? a : b; }
29 template<class T> T GCD(T a, T b) { return b ? GCD(b, a%b) : a; }
30 template<class T> T LCM(T a, T b) { return a / GCD(a,b) * b;    }
31 
32 //typedef __int64 LL;
33 //typedef long long LL;
34 const int MAXN = 10005;
35 const int MAXM = 20005;
36 const double eps = 1e-13;
37 //const LL MOD = 1000000007;
38 
39 int N;
40 int head[MAXN], next[MAXM], tot;
41 int  u[MAXM], v[MAXM], w[MAXM];
42 int fir[MAXN], sec[MAXN], ans[MAXN];
43 
44 void addEdge(int U, int V, int W)
45 {
46     u[tot] = U;
47     v[tot] = V;
48     w[tot] = W;
49     next[tot] = head[U];
50     head[U] = tot;
51     tot ++;
52 }
53 
54 int dfs1(int x, int fa)
55 {
56     fir[x] = sec[x] = 0;
57     for(int e = head[x]; e != -1; e = next[e]) if(v[e] != fa)
58     {
59         int dis = dfs1(v[e], x) + w[e];
60         if(dis >= fir[x]) { sec[x] = fir[x]; fir[x] = dis; }
61         else if(dis > sec[x]) sec[x] = dis;
62     }
63     return fir[x];
64 }
65 
66 void dfs2(int x, int fa, int dis)
67 {
68     ans[x] = MAX(fir[x], dis);
69     for(int e = head[x]; e != -1; e = next[e]) if(v[e] != fa)
70     {
71         int y = v[e];
72         if(fir[y] + w[e] == fir[x])
73             dfs2(y, x, MAX( dis, sec[x]) + w[e] );
74         else
75             dfs2(y, x, MAX( dis, fir[x]) + w[e] );
76     }
77 }
78 
79 int main()
80 {
81 
82     while(~scanf("%d", &N))
83     {
84         tot = 0;
85         mem1(head);
86         int V, W;
87         for(int i = 2; i <= N; i ++)
88         {
89             scanf("%d %d", &V, &W);
90             addEdge(i, V, W);
91             addEdge(V, i, W);
92         }
93         dfs1(1, 1);
94         dfs2(1, 1, 0);
95         for(int i = 1; i <= N; i ++ )
96             printf("%d
", ans[i]);
97     }
98     return 0;
99 }
    View Code

    F:HDU 4539

    最原始最薄里的状压DP  题解

      1 //#pragma comment(linker,"/STACK:102400000,102400000")
  2 #include <map>
  3 #include <set>
  4 #include <stack>
  5 #include <queue>
  6 #include <cmath>
  7 #include <ctime>
  8 #include <vector>
  9 #include <cstdio>
 10 #include <cctype>
 11 #include <cstring>
 12 #include <cstdlib>
 13 #include <iostream>
 14 #include <algorithm>
 15 using namespace std;
 16 #define INF 1e8
 17 #define inf (-((LL)1<<40))
 18 #define lson k<<1, L, mid
 19 #define rson k<<1|1, mid+1, R
 20 #define mem0(a) memset(a,0,sizeof(a))
 21 #define mem1(a) memset(a,-1,sizeof(a))
 22 #define mem(a, b) memset(a, b, sizeof(a))
 23 #define FOPENIN(IN) freopen(IN, "r", stdin)
 24 #define FOPENOUT(OUT) freopen(OUT, "w", stdout)
 25 template<class T> T CMP_MIN(T a, T b) { return a < b; }
 26 template<class T> T CMP_MAX(T a, T b) { return a > b; }
 27 template<class T> T MAX(T a, T b) { return a > b ? a : b; }
 28 template<class T> T MIN(T a, T b) { return a < b ? a : b; }
 29 template<class T> T GCD(T a, T b) { return b ? GCD(b, a%b) : a; }
 30 template<class T> T LCM(T a, T b) { return a / GCD(a,b) * b;    }
 31 
 32 //typedef __int64 LL;
 33 //typedef long long LL;
 34 const int MAXN = 10000;
 35 const int MAXM = 100005;
 36 const double eps = 1e-13;
 37 //const LL MOD = 1000000007;
 38 
 39 int N, M;
 40 int ma[110];
 41 int dp[2][200][200];
 42 
 43 int stNum;
 44 int st[1000], num[1000];
 45 
 46 int judge(int x)
 47 {
 48     if(x & (x<<2)) return 0;
 49     return 1;
 50 }
 51 
 52 int get1(int x)
 53 {
 54     int ret = 0;
 55     while(x)
 56     {
 57         ret += x & 1;
 58         x >>= 1;
 59     }
 60     return ret;
 61 }
 62 
 63 void init()
 64 {
 65     mem1(dp);mem0(ma);
 66     stNum = 0;
 67     for(int i=0;i<(1<<M);i++) if(judge(i))
 68     {
 69         st[stNum] = i;
 70         num[stNum++] = get1(i);
 71     }
 72 }
 73 
 74 
 75 int main()
 76 {
 77     //FOPENIN("in.txt");
 78     while(~scanf("%d %d%*c", &N, &M))
 79     {
 80         init();
 81         int x, cur = 0;
 82         for(int i=1;i<=N;i++)
 83             for(int j=0;j<M;j++) {
 84                 scanf("%d", &x);
 85                 if(x==0) ma[i] |= (1<<j);
 86             }
 87         for(int i=0;i<stNum;i++) {
 88             if(st[i] & ma[1]) continue;
 89             dp[cur][i][0] = num[i];
 90         }
 91         for(int r = 2; r <= N; r ++)
 92         {
 93             cur = !cur;
 94             for(int i = 0; i < stNum; i ++)
 95             {
 96                 if(st[i] & ma[r]) continue;
 97                 for(int j = 0; j < stNum; j ++ )
 98                 {
 99                     if(st[j] & ma[r-1]) continue;
100                     int p = (st[i]<<1) | (st[i]>>1);
101                     if(st[j] & p) continue;
102                     for(int k = 0; k < stNum; k ++) if(dp[!cur][j][k] != -1)
103                     {
104                         int pp = st[i] | ((st[j]<<1) | (st[j]>>1));
105                         if(st[k] & pp) continue;
106                         dp[cur][i][j] = MAX(dp[cur][i][j], dp[!cur][j][k] + num[i]);
107                     }
108 
109                 }
110             }
111         }
112         int ans = 0;
113         for(int i=0;i<stNum;i++) for(int j=0;j<stNum;j++)
114             ans = MAX(ans, dp[cur][i][j]);
115         printf("%d
", ans);
116     }
117     return 0;
118 }
119 
120 
121 /*
122 
123 6
124 3
125 2
126 12
127 
128 */
    View Code

    G:HDU 4035

    推公式很重要，是看别人做的。。。。题解

      1 //#pragma comment(linker,"/STACK:102400000,102400000")
  2 #include <map>
  3 #include <set>
  4 #include <stack>
  5 #include <queue>
  6 #include <cmath>
  7 #include <ctime>
  8 #include <vector>
  9 #include <cstdio>
 10 #include <cctype>
 11 #include <cstring>
 12 #include <cstdlib>
 13 #include <iostream>
 14 #include <algorithm>
 15 using namespace std;
 16 #define INF 1e8
 17 #define inf (-((LL)1<<40))
 18 #define lson k<<1, L, mid
 19 #define rson k<<1|1, mid+1, R
 20 #define mem0(a) memset(a,0,sizeof(a))
 21 #define mem1(a) memset(a,-1,sizeof(a))
 22 #define mem(a, b) memset(a, b, sizeof(a))
 23 #define FOPENIN(IN) freopen(IN, "r", stdin)
 24 #define FOPENOUT(OUT) freopen(OUT, "w", stdout)
 25 template<class T> T CMP_MIN(T a, T b) { return a < b; }
 26 template<class T> T CMP_MAX(T a, T b) { return a > b; }
 27 template<class T> T MAX(T a, T b) { return a > b ? a : b; }
 28 template<class T> T MIN(T a, T b) { return a < b ? a : b; }
 29 template<class T> T GCD(T a, T b) { return b ? GCD(b, a%b) : a; }
 30 template<class T> T LCM(T a, T b) { return a / GCD(a,b) * b;    }
 31 
 32 //typedef __int64 LL;
 33 //typedef long long LL;
 34 const int MAXN = 10005;
 35 const int MAXM = 100005;
 36 const double eps = 1e-10;
 37 //const LL MOD = 1000000007;
 38 
 39 int T, N;
 40 vector<int>v[MAXN];
 41 double k[MAXN], e[MAXN];
 42 double A[MAXN], B[MAXN], C[MAXN];
 43 
 44 
 45 void init()
 46 {
 47     int U, V;
 48     scanf("%d", &N);
 49     for(int i=0;i<=N;i++) v[i].clear();
 50     for(int i=0;i<N-1;i++)
 51     {
 52         scanf("%d %d", &U, &V);
 53         v[U].push_back(V);
 54         v[V].push_back(U);
 55     }
 56     for(int i=1;i<=N;i++)
 57     {
 58         scanf("%d %d", &U, &V);
 59         k[i] = (double)U / 100.0;
 60         e[i] = (double)V / 100.0;
 61     }
 62 }
 63 
 64 bool DFS(int x, int fa)
 65 {
 66     A[x] = k[x];
 67     B[x] = (1 - k[x] - e[x]) / v[x].size();
 68     C[x] = 1 - k[x] - e[x];
 69     if(v[x].size() == 1 && x != fa)
 70         return true;
 71     double temp = 0;
 72     for(int i = 0; i < v[x].size() ; i ++ )
 73     {
 74         int y = v[x][i];
 75         if(y == fa) continue;
 76         if(!DFS(y, x)) return false;
 77         A[x] += A[y] * B[x];
 78         C[x] += C[y] * B[x];
 79         temp += B[y] * B[x];
 80     }
 81     if(fabs(temp - 1.0) < eps) return false;
 82     A[x] = A[x] / (1 - temp);
 83     B[x] = B[x] / (1 - temp);
 84     C[x] = C[x] / (1 - temp);
 85     return true;
 86 }
 87 
 88 int main()
 89 {
 90     //FOPENIN("in.txt");
 91     scanf("%d", &T);
 92     for(int t = 1; t <= T; t ++ )
 93     {
 94         init();
 95         if( DFS(1, 1) && fabs(A[1] - 1.0) > eps )
 96         {
 97             printf("Case %d: %lf
", t, C[1] / (1 - A[1]));
 98         }
 99         else
100         {
101             printf("Case %d: impossible
", t);
102         }
103     }
104 }
    View Code

    I:HDU 1561

    树形DP，注意状态转化的过程  题解

     1 #include <map>
 2 #include <set>
 3 #include <stack>
 4 #include <queue>
 5 #include <cmath>
 6 #include <ctime>
 7 #include <vector>
 8 #include <cstdio>
 9 #include <cctype>
10 #include <cstring>
11 #include <cstdlib>
12 #include <iostream>
13 #include <algorithm>
14 using namespace std;
15 #define INF ((LL)100000000000000000)
16 #define inf (-((LL)1<<40))
17 #define lson k<<1, L, mid
18 #define rson k<<1|1, mid+1, R
19 #define mem0(a) memset(a,0,sizeof(a))
20 #define mem1(a) memset(a,-1,sizeof(a))
21 #define mem(a, b) memset(a, b, sizeof(a))
22 #define FOPENIN(IN) freopen(IN, "r", stdin)
23 #define FOPENOUT(OUT) freopen(OUT, "w", stdout)
24 template<class T> T CMP_MIN(T a, T b) { return a < b; }
25 template<class T> T CMP_MAX(T a, T b) { return a > b; }
26 template<class T> T MAX(T a, T b) { return a > b ? a : b; }
27 template<class T> T MIN(T a, T b) { return a < b ? a : b; }
28 template<class T> T GCD(T a, T b) { return b ? GCD(b, a%b) : a; }
29 template<class T> T LCM(T a, T b) { return a / GCD(a,b) * b;    }
30 
31 //typedef __int64 LL;
32 typedef long long LL;
33 const int MAXN = 255;
34 const int MAXM = 110000;
35 const double eps = 1e-12;
36 int dx[4] = {-1, 0, 0, 1};
37 int dy[4] = {0, -1, 1, 0};
38 
39 int N, M;
40 int G[MAXN][MAXN], vis[MAXN], num[MAXN];
41 int DP[MAXN][MAXN], D[MAXN];
42 
43 void DFS(int u)
44 {
45     vis[u] = 1;
46     DP[u][1] = num[u];
47     for(int i=1;i<=N;i++)  if(G[u][i])
48     {
49         if(!vis[i]) DFS(i);
50         for(int j=M;j>0;j--)//这里为了保证是先从父节点更新，需要逆序
51             for(int k=0;k<j;k++)//k<j保证父节点不会被更新掉
52                 DP[u][j] = MAX(DP[u][j], DP[u][j-k] + DP[i][k]);
53     }
54 }
55 
56 int main()
57 {
58     //FOPENIN("in.txt");
59     while(~scanf("%d %d", &N, &M) &&( N||M))
60     {
61         int a;mem0(G);mem0(D);mem0(vis);mem0(DP);
62         for(int i=1;i<=N;i++) {
63             scanf("%d %d", &a, &num[i]);
64             if(a != 0)G[a][i] = 1;
65             else D[i] = 1;
66         }
67         for(int i=1;i<=N;i++) if(!vis[i]){
68             DFS(i);
69             if(D[i]) for(int j=M;j>=0;j--)//同样需要逆序，可以取到0
70             {
71                 for(int k=0;k<=j;k++)
72                     DP[0][j] = MAX(DP[0][j], DP[0][j-k] + DP[i][k]);
73             }
74         }
75         printf("%d
", DP[0][M]);
76 
77     }
78     return 0;
79 }
    View Code

    J:HDU 4870

    1。高斯消元的做法

    2。公式推倒很重要

     1 #include <map>
 2 #include <set>
 3 #include <stack>
 4 #include <queue>
 5 #include <cmath>
 6 #include <ctime>
 7 #include <vector>
 8 #include <cstdio>
 9 #include <cctype>
10 #include <cstring>
11 #include <cstdlib>
12 #include <iostream>
13 #include <algorithm>
14 using namespace std;
15 #define INF ((LL)100000000000000000)
16 #define inf (-((LL)1<<40))
17 #define lson k<<1, L, mid
18 #define rson k<<1|1, mid+1, R
19 #define mem0(a) memset(a,0,sizeof(a))
20 #define mem1(a) memset(a,-1,sizeof(a))
21 #define mem(a, b) memset(a, b, sizeof(a))
22 #define FOPENIN(IN) freopen(IN, "r", stdin)
23 #define FOPENOUT(OUT) freopen(OUT, "w", stdout)
24 template<class T> T CMP_MIN(T a, T b) { return a < b; }
25 template<class T> T CMP_MAX(T a, T b) { return a > b; }
26 template<class T> T MAX(T a, T b) { return a > b ? a : b; }
27 template<class T> T MIN(T a, T b) { return a < b ? a : b; }
28 template<class T> T GCD(T a, T b) { return b ? GCD(b, a%b) : a; }
29 template<class T> T LCM(T a, T b) { return a / GCD(a,b) * b;    }
30 
31 //typedef __int64 LL;
32 typedef long long LL;
33 const int MAXN = 255;
34 const int MAXM = 110000;
35 const double eps = 1e-12;
36 
37 double t[30];
38 
39 int main()
40 {
41     //FOPENIN("in.txt");
42     double p;
43     while(~scanf("%lf", &p))
44     {
45         t[0] = 0;
46         t[1] = 1 / p;
47         t[2] = 1 / p + 1 / p / p;
48         for(int i=3;i<=20;i++)
49         {
50             t[i] = 1 / p * t[i-1] + 1 / p - (1-p) / p * t[i-3];
51         }
52         double ans = 2 *t[19] + t[20] - t[19];
53         printf("%lf
", ans);
54     }
55     return 0;
56 }
    View Code

    K:POJ 1160

    我就喜欢暴力求解  题解

     1 #include <map>
 2 #include <set>
 3 #include <stack>
 4 #include <queue>
 5 #include <cmath>
 6 #include <ctime>
 7 #include <vector>
 8 #include <cstdio>
 9 #include <cctype>
10 #include <cstring>
11 #include <cstdlib>
12 #include <iostream>
13 #include <algorithm>
14 using namespace std;
15 #define INF 100000000
16 #define inf (-((LL)1<<40))
17 #define lson k<<1, L, mid
18 #define rson k<<1|1, mid+1, R
19 #define mem0(a) memset(a,0,sizeof(a))
20 #define mem1(a) memset(a,-1,sizeof(a))
21 #define mem(a, b) memset(a, b, sizeof(a))
22 #define FOPENIN(IN) freopen(IN, "r", stdin)
23 #define FOPENOUT(OUT) freopen(OUT, "w", stdout)
24 template<class T> T CMP_MIN ( T a, T b ) { return a < b;   }
25 template<class T> T CMP_MAX ( T a, T b ) { return a > b;   }
26 template<class T> T MAX ( T a, T b ) { return a > b ? a : b; }
27 template<class T> T MIN ( T a, T b ) { return a < b ? a : b; }
28 template<class T> T GCD ( T a, T b ) { return b ? GCD ( b, a % b ) : a; }
29 template<class T> T LCM ( T a, T b ) { return a / GCD ( a, b ) * b;       }
30 template<class T> T SWAP( T& a, T& b ) { T t = a; a = b;  b = t; }
31 
32 //typedef __int64 LL;
33 typedef long long LL;
34 const int MAXN = 255;
35 const int MAXM = 110000;
36 const double eps = 1e-12;
37 
38 int V, P;
39 int x[310], DP[3][35][310];
40 int dis[310][310], pre[310];
41 
42 void initDis()
43 {
44         mem0(dis);mem0(pre);
45         for(int i=1;i<=V;i++)
46         for(int j=i;j<=V;j++)
47         for(int k=i;k<=j;k++)
48         dis[i][j] += MIN(x[k]-x[i], x[j]-x[k]);
49         for(int i=1;i<=V;i++)for(int j=i;j>=1;j--)
50                 pre[i] += x[i] - x[j];
51 }
52 
53 int main()
54 {
55         //FOPENIN ( "in.txt" );
56        //FOPENOUT("out.txt");
57        while(~scanf("%d %d", &V, &P))
58        {
59                 for(int i=1;i<=V;i++)
60                         scanf("%d", &x[i]);
61                 initDis();
62                 for(int i=0;i<2;i++)
63                 for(int j=0;j<=MIN(i,P);j++)
64                 for(int k=0;k<=i;k++){
65                         DP[i][j][k] = INF;
66                 }
67                 int now = 0;
68                 for(int i=1;i<=V;i++)
69                 {
70                         now = !now;
71                         int s = 0;
72                         for(int j=1;j<=i;j++)   DP[now][1][j] = pre[j];
73                         for(int j=2;j<=MIN(i, P); j++)
74                         {
75                                 DP[now][j][i] = INF;
76                                 for(int k=j-1;k<i;k++)if(DP[!now][j-1][k] != INF)
77                                 {
78                                         DP[now][j][i] = MIN(DP[now][j][i], DP[now][j-1][k] + dis[k][i]);
79                                 }
80                                 for(int k=j;k<i;k++) DP[now][j][k] = DP[!now][j][k];
81                         }
82                 }
83                 int ans = INF;
84                 for(int k=P;k<=V;k++)if(DP[now][P][k] != INF)
85                 {
86                         int s = 0;
87                         for(int j = k + 1; j <= V; j ++ ) s += x[j] - x[k];
88                         ans = MIN(ans, DP[now][P][k] + s);
89                 }
90                 printf("%d
", ans);
91        }
92         return 0;
93 }
    View Code
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  • 原文地址：https://www.cnblogs.com/gj-Acit/p/3888501.html
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