割顶：
POJ1144：求割顶的数量
1 #include <iostream> 2 #include <string.h> 3 #include <cstdio> 4 #include <queue> 5 #include <math.h> 6 #include <cstring> 7 #include <algorithm> 8 #include <sstream> 9 10 #define SIGMA_SIZE 26 11 #pragma warning ( disable : 4996 ) 12 13 using namespace std; 14 typedef long long LL; 15 16 inline LL LMax(LL a,LL b) { return a>b?a:b; } 17 inline LL LMin(LL a,LL b) { return a>b?b:a; } 18 inline int Max(int a,int b) { return a>b?a:b; } 19 inline int Min(int a,int b) { return a>b?b:a; } 20 inline int gcd( int a, int b ) { return b==0?a:gcd(b,a%b); } 21 inline int lcm( int a, int b ) { return a/gcd(a,b)*b; } //a*b = gcd*lcm 22 const int inf = 0x3f3f3f3f; 23 const int mod = 7; 24 const int maxn = 105; 25 const int maxk = 200; 26 27 28 int N, dfs_clock; 29 vector<int> mmap[maxn]; 30 int low[maxn<<1], pre[maxn<<1]; 31 bool iscut[maxn]; 32 33 int dfs( int x, int fa ) 34 { 35 int lowu = pre[x] = ++dfs_clock; 36 int child = 0; 37 38 for (int i = 0; i < mmap[x].size(); i++ ) 39 { 40 int tmp = mmap[x][i]; 41 if ( !pre[tmp] ) 42 { 43 child++; 44 int lowv = dfs( tmp, x ); 45 lowu = Min(lowu, lowv); 46 47 if ( lowv >= pre[x] ) 48 iscut[x] = true; 49 } else if ( pre[tmp] < pre[x] && tmp != fa ) 50 lowu = Min(lowu, pre[tmp]); 51 } 52 53 if ( fa < 0 && child == 1 ) iscut[x] = 0; 54 55 low[x] = lowu; 56 return lowu; 57 } 58 59 void init() 60 { 61 memset( mmap, 0, sizeof(mmap) ); 62 memset( pre, 0, sizeof(pre) ); 63 memset( iscut, 0, sizeof(iscut) ); 64 65 for( int i = 0; i < maxn; i++ ) 66 mmap[i].clear(); 67 dfs_clock = 0; 68 } 69 70 int main() 71 { 72 int x, y; 73 string str; 74 stringstream ss; 75 76 while ( getline(cin, str) ) 77 { 78 init(); 79 ss.clear(); ss << str; 80 ss >> N; 81 if (!N) break; 82 83 84 while ( getline(cin, str) ) 85 { 86 87 ss.clear(); ss << str; 88 ss >> x; 89 90 if ( !x ) break; 91 while ( ss >> y ) 92 { mmap[x].push_back(y); mmap[y].push_back(x); } 93 } 94 95 dfs(1,-1); 96 97 int ans = 0; 98 for( int i = 1; i <= N; i++ ) 99 if ( iscut[i] ) ans++; 100 cout << ans << endl; 101 } 102 103 return 0; 104 }