凭什么？？（Dinic版本）

#include<iostream>
#include<cstdio>
#include<cstring>
#include<queue>

using namespace std;
const int N = 207;
typedef long long lli;

int n, m, S, T;
int x, y, z;

struct pot{
    int v, nxt;
    lli val;
}E[50*N];
int head[N], tot = 1;
inline void Add_edge(int u, int v, int val) {
    E[++tot].v = v;
    E[tot].val = val;
    E[tot].nxt = head[u];
    head[u] = tot;
}

int dep[N], cur[N];
inline bool bfs() {
    queue <int> q;
    q.push(S);
    memset(dep, 0, sizeof(dep));
    dep[S] = 1;

    int u, v;
    while(q.size()) {
        u = q.front();
        q.pop();

        for(int i=head[u];i;i=E[i].nxt) {
            v = E[i].v;
            if(dep[v] || !E[i].val) continue;
            dep[v] = dep[u] + 1;
            q.push(v);
            if(v == T) return true;
        }
    }
    return false;
}
inline lli dfs(int u, lli nowflow) {
    if(u == T) return nowflow;
    if(nowflow == 0) return 0;

    int v;
    lli sum = 0, f;

    for(int i=cur[u];i;i=E[i].nxt) {
        v = E[i].v;
        cur[u] = i;
        if(dep[v] != dep[u]+1 || !E[i].val) continue;
        f = dfs(v, min(E[i].val, nowflow));
        E[i].val -= f;
        E[i^1].val += f;
        sum += f;
        nowflow -= f;
    }
    return sum;
}

void Dinic() {
    lli ans = 0;
    while(bfs()) {
        memcpy(cur, head, sizeof(cur));
        ans += dfs(S, 0x3fffffffffffffff);
    }
    printf("%lld\n", ans);
}

int main() {

    scanf("%d%d%d%d", &n, &m, &S, &T);
    for(int i=1;i<=m;++i) {
        scanf("%d%d%d", &x, &y, &z);
        Add_edge(x, y, z);
        Add_edge(y, x, 0);
    }

    Dinic();

    return 0;
}

(无语子......)