网络流入门（EK算法）

#include <iostream>
#include <cstring>
#include <cstdio>
#include <queue>
using namespace std;
const int inf = 0x3f3f3f3f;
const int maxn = 220;
int G[maxn][maxn];//描绘整张图；
int flow[maxn];//从原点到当前点的流量；
int pre[maxn];//标记上一步的增广路是哪一条路；
int n, m;
queue<int>q;
int bfs(int s, int t)//找增广路
{
	while (!q.empty()) q.pop();
	memset(pre, -1, sizeof(pre));
	pre[s] = 0, flow[s] = inf;
	q.push(s);
	while (!q.empty())
	{
		int p = q.front();q.pop();
		if (p == t) break;
		for (int u = 1; u <= n; u++)
		{
			if (u != s && G[p][u] > 0 && pre[u] == -1)
			{
				pre[u] = p;
				flow[u] = min(flow[p], G[p][u]);
				q.push(u);
			}
		}
	}
	if (pre[t] == -1) return -1;
	return flow[t];
}
int EK(int s, int t)
{
	int delta = 0;//当前残余网络被更新了多少。
	int tot = 0;//总的最大值是多少。
	while (1)
	{
		delta = bfs(s, t);
		if (delta == -1) break;
		int p = t;
		while (p != s)
		{
			G[pre[p]][p] -= delta;
			G[p][pre[p]] += delta;
			p = pre[p];
		}
		tot += delta;
	}
	return tot;
}
int main()
{
	while (~scanf("%d%d", &m, &n))
	{
		int u, v, w;
		memset(G, 0, sizeof(G));
		memset(flow, 0, sizeof(flow));
		for (int i = 0; i < m; i++)
		{
			scanf("%d%d%d", &u, &v, &w);
			G[u][v] += w;
		}
		printf("%d\n", EK(1, n));
	}
	return 0;
}