poj3740 Easy Finding DLX

    跟上题差不多，还是一个01矩阵，问是否可以选出若干行使得每列恰有一个1。模型都给建好了，直接建表搜就可以了..

#include <iostream>
#include <cstdio>
#include <algorithm>
#include <cmath>
#include <cstring>
using namespace std;
typedef long long ll;
const int maxn=320*320;

struct DLX
{
    int col[maxn],row[maxn],ans[maxn];
    int S[maxn],H[maxn];
    int size,cnt;
    int U[maxn],R[maxn],D[maxn],L[maxn];
    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=U[c]; i!=c; i=U[i])
        {
            for (int j=R[i]; j!=i; j=R[j])
            {
                U[D[j]]=j;
                D[U[j]]=j;
                ++S[col[j]];
            }
        }
    }
    bool dance(int k)
    {
        int c=R[0];
        if (c==0)
        {
            cnt=k;
            return true;
        }
        for (int i=R[0]; i!=0; i=R[i])
        {
            if (S[c]>S[i]) c=i;
        }
        remove(c);
        for (int i=D[c]; i!=c; i=D[i])
        {
            ans[k]=row[i];
            for (int j=R[i]; j!=i; j=R[j]) remove(col[j]);
            if (dance(k+1)) return true;
            for (int j=R[i]; j!=i; j=R[j]) resume(col[j]);
        }
        resume(c);
        return false;
    }
    void init(int n)
    {
        for (int i=0; i<=n; i++)
        {
            S[i]=0;
            L[i]=i-1;
            R[i]=i+1;
            U[i]=D[i]=i;
        }
        L[0]=n;
        R[n]=0;
        size=n+1;
        memset(H,-1,sizeof H);
    }
    void link(int x,int y)
    {
        ++S[col[size]=y];
        row[size]=x;
        D[size]=D[y];
        U[D[y]]=size;
        U[size]=y;
        D[y]=size;
        if (H[x]<0) H[x]=L[size]=R[size]=size;
        else
        {
            R[size]=R[H[x]];
            L[R[H[x]]]=size;
            L[size]=H[x];
            R[H[x]]=size;
        }
        size++;
    }
}dlx;
int n,m,k,num;
int main()
{
//    freopen("in.txt","r",stdin);

    while (~scanf("%d%d",&m,&n))
    {
        dlx.init(n);
        for (int i=1; i<=m; i++)
        for (int j=1; j<=n; j++)
        {
            scanf("%d",&k);
            if (k)
            {
                dlx.link(i,j);
            }
        }
        if (dlx.dance(0))
        {
            puts("Yes, I found it");
        }
        else puts("It is impossible");
    }
    return 0;
}