Poj 1273 Drainage Ditches(最大流 Edmonds-Karp )

题目链接：poj1273 Drainage Ditches

呜呜，今天自学网络流，看了EK算法，学的晕晕的，留个简单模板题来作纪念、、、

#include<cstdio>
#include<vector>
#include<queue>
#include<cstring>
#include<set>
#include<algorithm>
#define CLR(a,b) memset((a),(b),sizeof((a)))
using namespace std;

const int N = 201;
const int inf = 0x3f3f3f3f;
int n, m;
int g[N][N];//i到j的容量
int pre[N];//i的前驱节点
bool vis[N];
int flow[N][N];//从i到j的流量
int a[N];//从源点到i节点的最小残留量

int Edmonds_Karp(int st, int ed){
    int u, v;
    int f = 0;//最大流
    queue<int>q;//bfs找增广路
    while(1){
        CLR(vis, 0); CLR(a, 0);//每找一次记得初始化
        q.push(st);
        vis[st] = 1;
        a[st] = inf;
        while(!q.empty()){
            u = q.front(); q.pop();
            for(v = 1; v <= n; ++v){
                if(!vis[v] && g[u][v] > flow[u][v]){
                    q.push(v);
                    pre[v] = u;
                    vis[v] = 1;
                    a[v] = min(a[u], g[u][v] - flow[u][v]);
                }
            }
        }
        if(a[ed] == 0) break;//当前已经是最大流
        f += a[ed];
        for(u = ed; u != st; u = pre[u]){
            flow[pre[u]][u] += a[ed];
            flow[u][pre[u]] -= a[ed];
        }

    }
    return f;
}
int main(){
    int i, j, k, a, b, c;
    while(scanf("%d %d", &m, &n)==2){
        CLR(g, 0); CLR(flow, 0);
        for(i = 0; i < m; ++i){
            scanf("%d %d %d", &a, &b, &c);
            g[a][b] += c;//可能有重边
        }
        int max_flow = Edmonds_Karp(1, n);
        printf("%d
", max_flow);
    }
    return 0;
}