洛谷 P3376 【模板】网络最大流

参考链接:https://www.cnblogs.com/widerg/p/9387909.html

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#include<iostream>
#include<algorithm>
#include<queue>
#include<cstring>
using namespace std;
const int eN = 100005;
const int vN = 10005;
const int INF = 0x7f7f7f7f;
int n, m, s, t;
int ePtr = -1; //e的实际存储只能从偶数号顶点开始,奇数号顶点存储反向边
int to[eN<<1], nxt[eN<<1], value[eN<<1];
int head[vN], dis[vN];
inline void createEdge(int u, int v, int w) {
    to[++ePtr] = v;
    value[ePtr] = w;
    nxt[ePtr] = head[u];
    head[u] = ePtr;
}
bool bfs(int s, int t) {
    queue<int> q;
    memset(dis, 0x7f, sizeof(dis));
    dis[s] = 0;
    q.push(s);
    while (!q.empty()) {
        int x = q.front();
        q.pop();
        for (int i = head[x]; ~i; i = nxt[i]) {
            int dest = to[i];
            if (dis[dest] == INF && value[i] != 0) {
                dis[dest] = dis[x] + 1;
                q.push(dest);
            }
        }
    }
    return dis[t] != INF;
}
int dfs(int x, int t, int maxflow) {
    if (x == t)return maxflow;
    int ans = 0;
    for (int i = head[x]; ~i; i = nxt[i]) {
        int dest = to[i];
        if (dis[dest] != dis[x] + 1 || value[i] == 0 || ans >= maxflow)continue;
        int f = dfs(dest, t, min(value[i], maxflow - ans));
        value[i] -= f;
        value[i ^ 1] += f;
        ans += f;
    }
    return ans;
}
int dinic(int s, int t) {
    int ans = 0;
    while (bfs(s, t))ans += dfs(s, t, INF);
    return ans;
}
int main() {
    memset(head, -1, sizeof(head));
    scanf("%d%d%d%d", &n, &m, &s, &t);
    for (int i = 1; i <= m; i++) {
        int u, v, w;
        scanf("%d%d%d", &u, &v, &w);
        createEdge(u, v, w);
        createEdge(v, u, 0);//第0号边被占用,这条语句为下一个边留下空间
    }
    printf("%d", dinic(s, t));
}

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