Dinic：

1 #include 
      
        2  3 using namespace std; 4  5 const int MAXN = 1e5 + 5, inf = 0x7f7f7f7f; 6  7 struct edge { 8     int to, nxt, cap; 9 } edges[MAXN << 1];10 11 int head[MAXN], level[MAXN], cur[MAXN], n, m, s, t, cnt = 0;12 13 inline void addedge(int from, int to, int cap) {14     edges[cnt].to = to, edges[cnt].nxt = head[from];15     edges[cnt].cap = cap, head[from] = cnt++;16     edges[cnt].to = from, edges[cnt].nxt = head[to];17     edges[cnt].cap = 0, head[to] = cnt++;18 }19 20 queue
       
         que;21 int getlevel() {22     memset(level, 0, sizeof(level));23     for(int i = 1; i <= n; i++) cur[i] = head[i];24     level[s] = 1; que.push(s);25     while(!que.empty()) {26         for(int i = head[que.front()]; i != -1; i = edges[i].nxt)27             if(!level[edges[i].to] && edges[i].cap) {28                 level[edges[i].to] = level[que.front()] + 1;29                 que.push(edges[i].to);30             }31         que.pop();32     }33     return level[t];34 }35 36 int impflow(int now, int ff) {37     if(now == t) return ff;38     int flow = 0, resi;39     for(int &i = cur[now]; i != -1; i = edges[i].nxt)40         if(edges[i].cap && level[edges[i].to] > level[now] &&41             (resi = impflow(edges[i].to, min(ff, edges[i].cap)))) {42             edges[i].cap -= resi; edges[i ^ 1].cap += resi;43             flow += resi; ff -= resi;44             if(!ff) break;45         }46     return flow;47 }48 49 int getmaxflow() {50     int maxflow = 0;51     while(getlevel()) maxflow += impflow(s, inf);52     return maxflow;53 }54 55 int main() {56     memset(head, 0xff, sizeof(head));57     int x, y, z;58     scanf("%d%d%d%d", &n, &m, &s, &t);59     while(m--) scanf("%d%d%d", &x, &y, &z), addedge(x, y, z);60     printf("%d\n", getmaxflow());61     return 0;62 }