poj1273 最大流模板 Edmond_karp算法

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Edmond_karp算法：

#include<cstdio>#include<cstring>#include<iostream>#include<algorithm>#include<cmath>#include<queue>using namespace std;const int maxn = 200 + 5;const int inf = 0x7f7f7f7f;int pre[maxn], c[maxn][maxn], flow[maxn];int ans;int bfs(int s, int t){    queue<int> q;    memset(pre, -1, sizeof(pre));    memset(flow, 0, sizeof(flow));    q.push(s);    flow[s] = inf;    while(!q.empty())    {        int u = q.front();        q.pop();        if (u == t) break;        for (int i = 1; i <= t; i++)        {            if (!flow[i] && c[u][i] > 0)            {                pre[i] = u;                q.push(i);                flow[i] = min(flow[u], c[u][i]);//s-v路径上的最小残量            }        }    }    if (pre[t] == -1) return -1;    return 1;}int Edmond_karp(int s, int t){    int max_flow = 0;    while (bfs(s, t) != -1)//寻找增广路径    {        max_flow += flow[t];        int k = t;        while  (pre[k] != -1)        {            c[pre[k]][k] -= flow[t];//更新正向流量            c[k][pre[k]] += flow[t];//更新反向流量            k = pre[k];        }    }    return max_flow;}int main(){    //freopen("input.txt", "r", stdin);    int n, m;    while (cin >> n >> m)    {        memset(c, 0, sizeof(c));//初始化        for (int i = 0; i < n; i++)        {            int u, v, x;            scanf("%d%d%d", &u, &v, &x);            c[u][v] += x;        }        printf("%d\n", Edmond_karp(1, m));    }    return 0;}

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