HDU-4665 Unshuffle 搜索 | 2-SAT

　　题目链接：http://acm.hdu.edu.cn/showproblem.php?pid=4665

　　本题的2-SAT建图颇为复杂，有时间再来填坑（自己写的一直挂着，标程建图太复杂了）。。。然后用暴力搜索，用一个栈保存第一个序列就可以了，因为题目是SPG，并且重复的最多只有四个，所以搜索很好过。。

//STATUS:C++_AC_62MS_276KB
#include <functional>
#include <algorithm>
#include <iostream>
//#include <ext/rope>
#include <fstream>
#include <sstream>
#include <iomanip>
#include <numeric>
#include <cstring>
#include <cassert>
#include <cstdio>
#include <string>
#include <vector>
#include <bitset>
#include <queue>
#include <stack>
#include <cmath>
#include <ctime>
#include <list>
#include <set>
#include <map>
using namespace std;
//#pragma comment(linker,"/STACK:102400000,102400000")
//using namespace __gnu_cxx;
//define
#define pii pair<int,int>
#define mem(a,b) memset(a,b,sizeof(a))
#define lson l,mid,rt<<1
#define rson mid+1,r,rt<<1|1
#define PI acos(-1.0)
//typedef
typedef __int64 LL;
typedef unsigned __int64 ULL;
//const
const int N=2010;
const int INF=0x3f3f3f3f;
const int MOD= 1000000007,STA=8000010;
const LL LNF=1LL<<55;
const double EPS=1e-9;
const double OO=1e30;
const int dx[4]={-1,0,1,0};
const int dy[4]={0,1,0,-1};
const int day[13]={0,31,28,31,30,31,30,31,31,30,31,30,31};
//Daily Use ...
inline int sign(double x){return (x>EPS)-(x<-EPS);}
template<class T> T gcd(T a,T b){return b?gcd(b,a%b):a;}
template<class T> T lcm(T a,T b){return a/gcd(a,b)*b;}
template<class T> inline T lcm(T a,T b,T d){return a/d*b;}
template<class T> inline T Min(T a,T b){return a<b?a:b;}
template<class T> inline T Max(T a,T b){return a>b?a:b;}
template<class T> inline T Min(T a,T b,T c){return min(min(a, b),c);}
template<class T> inline T Max(T a,T b,T c){return max(max(a, b),c);}
template<class T> inline T Min(T a,T b,T c,T d){return min(min(a, b),min(c,d));}
template<class T> inline T Max(T a,T b,T c,T d){return max(max(a, b),max(c,d));}
//End

int num[N],sta[N],vis[N];
int T,n,top1,top2,mid;

bool dfs(int u)
{
    if(top2==mid)return true;
    if(top1<mid){
        vis[u]=0;
        sta[top1++]=num[u];
        if(dfs(u+1))return true;
        top1--;
    }
    if(num[u]==sta[top2]){
        vis[u]=1;
        top2++;
        if(dfs(u+1))return true;
        vis[u]=0;
        top2--;
    }
    return false;
}

int main(){
 //   freopen("in.txt","r",stdin);
    int i,j;
    scanf("%d",&T);
    while(T--)
    {
        scanf("%d",&n);
        mid=n>>1;
        for(i=0;i<n;i++)
            scanf("%d",&num[i]);

        top1=top2=0;
        dfs(0);

        for(i=0;i<n;i++)
            printf("%d",vis[i]);
        putchar('
');
    }
    return 0;
}

2-SAT(WA):

/*   WA   */
#include <functional>
#include <algorithm>
#include <iostream>
//#include <ext/rope>
#include <fstream>
#include <sstream>
#include <iomanip>
#include <numeric>
#include <cstring>
#include <cassert>
#include <cstdio>
#include <string>
#include <vector>
#include <bitset>
#include <queue>
#include <stack>
#include <cmath>
#include <ctime>
#include <list>
#include <set>
#include <map>
using namespace std;
//#pragma comment(linker,"/STACK:102400000,102400000")
//using namespace __gnu_cxx;
//define
#define pii pair<int,int>
#define mem(a,b) memset(a,b,sizeof(a))
#define lson l,mid,rt<<1
#define rson mid+1,r,rt<<1|1
#define PI acos(-1.0)
//typedef
typedef __int64 LL;
typedef unsigned __int64 ULL;
//const
const int N=2010;
const int INF=0x3f3f3f3f;
const int MOD= 1000000007,STA=8000010;
const LL LNF=1LL<<55;
const double EPS=1e-9;
const double OO=1e30;
const int dx[4]={-1,0,1,0};
const int dy[4]={0,1,0,-1};
const int day[13]={0,31,28,31,30,31,30,31,31,30,31,30,31};
//Daily Use ...
inline int sign(double x){return (x>EPS)-(x<-EPS);}
template<class T> T gcd(T a,T b){return b?gcd(b,a%b):a;}
template<class T> T lcm(T a,T b){return a/gcd(a,b)*b;}
template<class T> inline T lcm(T a,T b,T d){return a/d*b;}
template<class T> inline T Min(T a,T b){return a<b?a:b;}
template<class T> inline T Max(T a,T b){return a>b?a:b;}
template<class T> inline T Min(T a,T b,T c){return min(min(a, b),c);}
template<class T> inline T Max(T a,T b,T c){return max(max(a, b),c);}
template<class T> inline T Min(T a,T b,T c,T d){return min(min(a, b),min(c,d));}
template<class T> inline T Max(T a,T b,T c,T d){return max(max(a, b),max(c,d));}
//End

struct Edge{
    int u,v;
}e[N<<4];

int first[N<<1],next[N<<4],vis[N<<1],S[N<<1];
int num[N];
int T,n,mt,cnt;

void adde(int a,int b)
{
    e[mt].u=a,e[mt].v=b;
    next[mt]=first[a];first[a]=mt++;
}

int dfs(int u)
{
    if(vis[u^1])return 0;
    if(vis[u])return 1;
    int i;
    vis[u]=1;
    S[cnt++]=u;
    for(i=first[u];i!=-1;i=next[i]){
        if(!dfs(e[i].v))return 0;
    }
    return 1;
}

int Twosat()
{
    int i,j;
    for(i=0;i<n;i+=2){
        if(vis[i] || vis[i^1])continue;
        cnt=0;
        if(!dfs(i)){
            while(cnt)vis[S[--cnt]]=0;
            if(!dfs(i^1))return 0;
        }
    }
    return 1;
}

int cnt2[N],tot[N],w[N][4];
void Init()
{
    int i,j,t;
    mt=0;mem(vis,0);
    mem(first,-1);
    mem(tot,0);
    for(i=0;i<n;i++)w[num[i]][tot[num[i]]++]=i;
    mem(cnt2,0);
    for(i=0;i<n;i++){
        t=num[i];
        cnt2[t]++;
        if(cnt2[t]==1){
            adde((i<<1)^1,i<<1);
            adde(i<<1,(w[t][tot[t]-1]<<1)^1);
            adde(w[t][tot[t]-1]<<1,(i<<1)^1);
            if(tot[t]==4){
                for(j=w[t][1]+1;j<n;j++){
                    if(w[num[j]][1]==j && w[num[j]][0]<j && w[num[j]][0]>i){
                        adde(i<<1,(w[t][1]<<1)^1);
                        break;
                    }
                }
            }
        }
        else if(cnt2[t]==3){
            adde(w[t][1]<<1,(w[t][2]<<1)^1);
            adde((w[t][1]<<1)^1,w[t][2]<<1);
            adde(w[t][2]<<1,(w[t][1]<<1)^1);
            adde((w[t][2]<<1)^1,w[t][1]<<1);
        }
    }
}

int main(){
    freopen("in.txt","r",stdin);
    int i,j;
    scanf("%d",&T);
    while(T--)
    {
        scanf("%d",&n);
        for(i=0;i<n;i++)
            scanf("%d",&num[i]);

        Init();
        n<<=1;
        int t=Twosat();
    //    printf("%d
",t);

        for(i=0;i<n;i+=2)
            printf("%d",vis[i]);
        putchar('
');
    }
    return 0;
}