AcWing 進階課知識點模板梳理

EK 求最大流

點選檢視程式碼

#include <bits/stdc++.h>
#define int long long
using namespace std;
const int N = 1005, M = 20005,INF=1e8;
int n, m, S, T;
int h[N], e[M], f[M], ne[M], idx;
int q[N], d[N], pre[N];
bool st[N];
void add(int a,int b,int c){
    e[idx] = b, f[idx] = c, ne[idx] = h[a], h[a] = idx++;
    e[idx] = a, f[idx] = 0, ne[idx] = h[b], h[b] = idx++;
}

bool bfs(){
    int hh = 0, tt = 0;
    memset(st, 0, sizeof(st));
    q[0] = S, st[S] = 1,d[S] = INF;

    while(hh<=tt){
        int t = q[hh++];
        for (int i = h[t]; ~i;i=ne[i]){
            int ver = e[i];
            if(!st[ver]&&f[i]){
                st[ver] = 1;
                d[ver] = min(d[t], f[i]);
                pre[ver] = i;
                if(ver==T) return 1;
                 q[++tt] = ver;
            }
        }
    }
    return 0;
}
int EK(){
    int r = 0; 
    while(bfs()){
        r += d[T];
        for (int i = T; i != S;i=e[pre[i]^1])
            f[pre[i]] -= d[T], f[pre[i]^1] += d[T];
    }
    return r;
}
int main(){
    memset(h, -1, sizeof(h));
    cin >> n >> m >> S >> T;
    while(m--){
        int a, b, c;
        cin >> a >> b >> c;
        add(a, b, c);
        
    }
    cout << EK() << endl;
    return 0;
}