joyoi1957 「Poetize5」Vani和Cl2捉迷藏

Posted 2020-10-30 poorpool

最小路径可重点覆盖。先传递闭包，然后拆点，\(n-\)最大匹配，看算法竞赛进阶指南。

#include <iostream>
#include <cstring>
#include <cstdio>
using namespace std;
int n, m, uu, vv, mat[205], ans;
bool w[205][205], vis[205];
bool hung(int x){
    for(int i=1; i<=n; i++)
        if(w[x][i]){
            if(vis[i])  continue;
            vis[i] = true;
            if(!mat[i] || hung(mat[i])){
                mat[i] = x;
                return true;
            }
        }
    return false;
}
int main(){
    cin>>n>>m;
    for(int i=1; i<=m; i++){
        scanf("%d %d", &uu, &vv);
        w[uu][vv] = true;
    }
    for(int k=1; k<=n; k++)
        for(int i=1; i<=n; i++)
            for(int j=1; j<=n; j++)
                w[i][j] |= w[i][k] & w[k][j];
    for(int i=1; i<=n; i++){
        memset(vis, 0, sizeof(vis));
        if(hung(i)) ans++;
    }
    cout<<n-ans<<endl;
    return 0;
}