HDU 1532 Drainage Ditches——最大流EK算法

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

using namespace std;

const int INF = 0x3f3f3f3f;
const int maxn = 1000 + 10;

struct Node {
    int to;
    int cap;
    int rev;
};

vector<Node> v[maxn];
bool used[maxn];

void add_node(int from, int to, int cap) {
    v[from].push_back((Node){to, cap, v[to].size()});
    v[to].push_back((Node){from, 0, v[from].size() - 1});
}

int dfs(int s, int t, int f) {
    if (s == t) return f;
    used[s] = true;
    for (int i = 0; i < v[s].size(); i++) {
        Node &temp = v[s][i];
        if (used[temp.to] == false && temp.cap > 0) {
            int d = dfs(temp.to, t, min(f, temp.cap));
            if (d > 0) {
                temp.cap -= d;
                v[temp.to][temp.rev].cap += d;
                return d;
            }
        }
    }
    return 0;
}

int max_flow(int s, int t) {
    int flow = 0;
    while (true) {
        memset(used, false, sizeof(used));
        int f = dfs(s, t, INF);
        if (f == 0) return flow;
        flow += f;
    }
}

int main()
{
    int n, m;
    while (scanf("%d %d", &n, &m) == 2) {
        memset(v, 0, sizeof(v));
        for (int i = 0; i < n; i++) {
            int x, y, z;
            scanf("%d %d %d", &x, &y, &z);
            add_node(x, y, z);
        }
        printf("%d\n", max_flow(1, m));
    }
    return 0;
}