POJ 3740 Easy Finding DLX

题意：给你一个0,1矩阵 ，求精确覆盖

解题思路：

DLX

解题代码：

// File Name: poj3740.cpp
// Author: darkdream
// Created Time: 2014年10月04日 星期六 20时06分31秒

#include<vector>
#include<list>
#include<map>
#include<set>
#include<deque>
#include<stack>
#include<bitset>
#include<algorithm>
#include<functional>
#include<numeric>
#include<utility>
#include<sstream>
#include<iostream>
#include<iomanip>
#include<cstdio>
#include<cmath>
#include<cstdlib>
#include<cstring>
#include<ctime>
#define LL long long

using namespace std;
const int maxnode = 50000;
const int MaxN = 18;
const int MaxM = 400;
struct DLX
{
    int n , m , size;
    int U[maxnode],D[maxnode],L[maxnode],R[maxnode],Row[maxnode],Col[maxnode];
    int H[MaxN],S[MaxM];
    void init(int _n,int _m)
    {
       n = _n;
       m = _m;
       for(int i = 0 ;i <= m;i ++)
       {
           S[i] = 0 ; 
           U[i] = i ; 
           D[i] = i ; 
           L[i] = i-1;
           R[i] = i+1;
       }
       size = m ; 
       L[0] = m; 
       R[m] = 0 ;
       memset(H,-1,sizeof(H));
    }
    void Link(int r, int c)
    {
        ++S[Col[++size] = c];
        Row[size] = r; 
        D[size] = D[c];
        U[D[c]] = size;
        U[size] = c; 
        D[c] = size ;
        if(H[r] < 0)  H[r] = L[size] = R[size] = size;
        else{
          R[size] = R[H[r]];
          L[R[H[r]]] = size;
          L[size] = H[r];
          R[H[r]] = size;
        }
    }
    void remove(int c)
    {
      L[R[c]] = L[c];
      R[L[c]] = R[c];
      for(int i = D[c]; i != c ;i = D[i])
          for(int j = R[i]; j != i ;j = R[j])
          {
               U[D[j]] = U[j];
               D[U[j]] = D[j];
               --S[Col[j]];
          }
    }
    void resume(int c)
    {
       L[R[c]] = c; 
       R[L[c]] = c; 
       for(int i = D[c];i != c;i = D[i])
           for(int j = R[i]; j != i ;j = R[j])
           {
              U[D[j]] = j ; 
              D[U[j]] = j; 
              ++ S[Col[j]];
           }
    }
    bool Dance()
    {
       if(R[0] == 0 )
       {
         return true;
       }
       int c = R[0];
       for(int i = R[c];i != 0 ;i = R[i])
           if(S[i] < S[c])
               c = i ; 
       remove(c);
       for(int i = D[c];i != c;i = D[i])
       {
           for(int j = R[i];j != i ;j = R[j]) remove(Col[j]);
           if(Dance()) return true;
           for(int j = R[i];j != i; j = R[j]) resume(Col[j]);
       }
       resume(c);
       return false;
    }
};

DLX g; 
int main(){
    int n , m ; 
    while(scanf("%d %d",&n,&m) != EOF)
    {
       g.init(n,m);
       int t ;
       for(int i = 1;i <= n;i ++)
           for(int j = 1;j <= m;j ++)
           {
              scanf("%d",&t);
              if(t)
                g.Link(i,j);
           }
       if(g.Dance()) 
           printf("Yes, I found it
");
       else printf("It is impossible
");
    }
return 0;
}