HDU 1281 棋盘游戏

题目大意：略

 

题目思路： 先求出一个最大匹配，再枚举每条边。（刚开始感觉好暴力...........但事实是只用了31ms  无语了）

 

#include<stdio.h>
#include<string.h>
#include<algorithm>
#include<iostream>
using namespace std;
#define maxn 1500
bool G[maxn][maxn], vis[maxn];
int P[maxn];
int n, m, cas = 1;

bool Find(int u)
{
    for(int i=1; i<=m; i++)
    {
        if(G[u][i] && !vis[i])
        {
            vis[i] = true;
            if(P[i] == -1 || Find(P[i]) )
            {
                P[i] = u;
                return true;
            }
        }
    }
    return false;
}

int GetAns()
{
    memset(P, -1, sizeof(P));
    int ans = 0;
    for(int i=1; i<=n; i++)
    {
        memset(vis, false, sizeof(vis));
        if( Find(i) )
            ans ++;
    }
    return ans;
}

void solve()
{
    int Imp = 0, ans;

    ans = GetAns();

    for(int i=1; i<=n; i++)
    {
        for(int j=1; j<=m; j++)
        {
            if(!G[i][j])
                continue;

            G[i][j] = false;
            if(GetAns() < ans) Imp ++;
            G[i][j] = true;
        }
    }
    printf("Board %d have %d important blanks for %d chessmen.\n",cas ++, Imp, ans);
}

int main()
{
    int Q;
    while(scanf("%d %d %d",&n, &m, &Q) != EOF)
    {
        memset(G, false, sizeof(G));
        while(Q --)
        {
            int a, b;
            scanf("%d %d", &a, &b);
            G[a][b] = true;
        }
        solve();
    }
    return 0;
}