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Posted 2020-10-24 js2xxx

#include <iostream>
#include <vector>
#include <map>
#include <queue>
#include <cstring>

using namespace std;

int n, m, src, dst, depth[10001], ec;
struct EDGE
{
    int to, weight;
    EDGE() { }
    EDGE(int t, int w) { to = t, weight = w; }
} edge[100001];
vector<int> g[10001];

void insert_edge(int s, int d, int w)
{
    edge[ec] = EDGE(d, w);
    g[s].push_back(ec++);
    edge[ec] = EDGE(s, 0);
    g[d].push_back(ec++);
}

bool bfs()
{
    memset(depth, 0, sizeof(depth));
    queue<int> q; EDGE e;
    depth[src] = 1;
    q.push(src);
    do
    {
        int p = q.front();
        q.pop();
        for(int i = 0; i < g[p].size(); i++)
        {
            e = edge[g[p][i]];
            if(e.weight > 0 && !depth[e.to])
            {
                depth[e.to] = depth[p] + 1;
                q.push(e.to);
            }
        }
    } while(!q.empty());
    return depth[dst] > 0;
}

int dfs(int p, int cur)
{
    if(p == dst) return cur;
    EDGE e;
    for(int i = 0; i < g[p].size(); i++)
    {
        e = edge[g[p][i]];
        if(depth[e.to] == depth[p] + 1 && e.weight)
        {
            int c = dfs(e.to, min(cur, e.weight));
            if(c > 0)
            {
                edge[g[p][i]].weight -= c;
                edge[g[p][i] ^ 1].weight += c;
                return c;
            }
        }
    }
    return 0;
}

int main()
{
    int s, d, w;
    scanf("%d%d%d%d", &n, &m, &src, &dst);
    for(int i = 1; i <= m; i++)
    {
        scanf("%d%d%d", &s, &d, &w);
        insert_edge(s, d, w);
    }
    int s = 0;
    while(bfs())
        s += dfs(src, 1e9 - 1);
    printf("%d\n", s);
}