hdu 3549 Flow Problem (最大流)

裸最大流，做模板用

m条边，n个点，求最大流

#include <iostream>
#include <cstdio>
#include <cstring>
#include <queue>
#include <algorithm>

using namespace std;

const int N = 20;
const int INF = 0x7fffffff;

int flow[N];
int cap[N][N];
int pre[N];

queue<int>q;

int m, n;

int BFS(int src, int des)
{
    while (!q.empty()) q.pop();
    for (int i = 1; i <= n; ++i) pre[i] = -1;
    flow[src] = INF;
    pre[src] = 0;
    q.push(src);
    while (!q.empty()) {
        int index = q.front();
        q.pop();
        if (index == des) break;
        for (int i = 1; i <= n; ++i) {
            if (pre[i] == -1 && cap[index][i] > 0) {
                pre[i] = index;
                flow[i] = min(cap[index][i], flow[index]);
                q.push(i);
            }
        }
    }
    if (pre[des] == -1) return -1;
    return flow[des];
}

int maxFlow(int src, int des)
{
    int ans = 0;
    int in = 0;
    while ((in = BFS(src, des)) != -1) {
        int k = des;
        while (k != src) {
            int last = pre[k];
            cap[last][k] -= in;
            cap[k][last] += in;
            k = last;
        }
        ans += in;
    }
    return ans;
}

int main()
{
    int t;
    int i, k;
    scanf("%d", &t);
    for (k = 1; k <= t; ++k) {
        memset(cap, 0, sizeof cap);
        memset(flow, 0, sizeof flow);
        scanf("%d%d", &n, &m);
        for (i = 0; i < m; ++i) {
            int a, b, c;
            scanf("%d%d%d", &a, &b, &c);
            cap[a][b] += c;
        }
        printf("Case %d: %d
", k, maxFlow(1, n));
    }
    return 0;
}