POJ-2594 Treasure Exploration 最小路径覆盖

//STATUS:G++_AC_1594MS_1700KB
#include<stdio.h>
#include<stdlib.h>
#include<string.h>
#include<math.h>
#include<iostream>
#include<string>
#include<algorithm>
#include<vector>
#include<queue>
#include<stack>
#include<map>
using namespace std;
#define LL long long
#define Max(a,b) ((a)>(b)?(a):(b))
#define Min(a,b) ((a)<(b)?(a):(b))
#define mem(a,b) memset(a,b,sizeof(a))
#define lson l,mid,rt<<1
#define rson mid+1,r,rt<<1|1
const int MAX=510,INF=200000000;

int g[MAX][MAX],y[MAX],vis[MAX];
int n,m;

int dfs(int u)
{
int v;
for(v=1;v<=n;v++){
if(g[u][v] && !vis[v]){
vis[v]=1;
if(!y[v] || dfs(y[v])){
y[v]=u;
return 1;
}
}
}
return 0;
}

int main()
{
//   freopen("in.txt","r",stdin);
int i,j,k,u,v,ans;
while(~scanf("%d%d",&n,&m) && (n||m))
{
ans=0;
mem(g,0);
mem(y,0);
for(i=0;i<m;i++){
scanf("%d%d",&u,&v);
g[u][v]=1;
}

for(k=1;k<=n;k++)
for(i=1;i<=n;i++)
for(j=1;j<=n;j++)
g[i][j]=g[i][j]||(g[i][k] && g[k][j]);

for(i=1;i<=n;i++){
mem(vis,0);
if(dfs(i))ans++;
}

printf("%d\n",n-ans);
}
}