luogu2740 [USACO4.2]草地排水Drainage Ditches 最大流EK

Posted 2020-10-18 poorpool

练一下最大流

#include <iostream>
#include <cstring>
#include <cstdio>
#include <queue>
using namespace std;
int n, m, ron[205][205], pre[205], uu, vv, ww, vis[205];
queue<int> d;
int ek(){
    int maxFlow=0;
    while(1){
        memset(vis, 0, sizeof(vis));
        vis[1] = 0x3f3f3f3f;
        d.push(1);
        while(!d.empty()){
            int x=d.front();
            d.pop();
            for(int i=1; i<=n; i++)
                if(!vis[i] && ron[x][i]>0){
                    vis[i] = min(vis[x], ron[x][i]);
                    pre[i] = x;
                    d.push(i);
                }
        }
        if(!vis[n]) break;
        maxFlow += vis[n];
        int hs=n;
        while(pre[hs]){
            ron[pre[hs]][hs] -= vis[n];
            ron[hs][pre[hs]] += vis[n];
            hs = pre[hs];
        }
    }
    return maxFlow;
}
int main(){
    cin>>m>>n;
    for(int i=1; i<=m; i++){
        scanf("%d %d %d", &uu, &vv, &ww);
        ron[uu][vv] += ww;
    }
    printf("%d\n", ek());
    return 0;
}