POJ1273Drainage Ditches(网络流入门题目）

#include <iostream>
#include <cstdio>
#include <cstring>
#include <algorithm>
#include <queue>
#include <cstdlib>
using namespace std;
const int INF = 0x7fffffff;
const int N = 210;
int map1[N][N];
int link[N];
int mi[N];
int n, m;
//EK算法
int bfs(int s) {
    queue<int> Q;
    memset(link, 0, sizeof(link));
    mi[s] = INF;
    Q.push(s);
    int u, v;
    while(!Q.empty()) {
        u = Q.front();
        Q.pop();
        for(v = 2; v <= n; v++) {
            if(map1[u][v]>0 && !link[v]) {
                mi[v] = min(mi[u], map1[u][v]);
                link[v] = u;
                if(v == n) { return mi[n]; }
                Q.push(v);
            }
        }
    }
    return 0;
}

void work() {
    int ans, now, pre, x;
    for(ans = 0; (x = bfs(1))!=0; ans+=x) {
        now = n;
        while(now != 1) {
            pre = link[now];
            map1[pre][now] -= x;
            map1[now][pre] += x;
            now = pre;
        }
    }
    printf("%d\n", ans);
}

int main() {
    int u, v, cost;
    while(scanf("%d%d", &m, &n) == 2) {
        memset(map1, 0, sizeof(map1));
        for(int i = 0; i < m; i++) {
            scanf("%d%d%d", &u, &v, &cost);
            map1[u][v] += cost;//处理重边。
        }
        work();
    }
}