新人求助，为何只有70分...

#include<iostream>
#include<cstring>
#include<math.h>
#include<stdlib.h>
#include<cstring>
#include<cstdio>
#include<utility>
#include<algorithm>
#include<queue>
using namespace std;
const int maxn=1e5+10;
int dep[maxn],head[maxn],vis[maxn];//层次 
int n,m,s,t;
const int inf=0x3f3f3f3f;
int maxflow=0;
int cnt=1;
struct node{
    int to,val,next;
}star[500100];
void add(int u,int v,int w){//前向星 
    star[cnt].to=v;
    star[cnt].val=w;
    star[cnt].next=head[u];
    head[u]=cnt++;
}
bool bfs(){//分层 
    memset(dep,inf,sizeof(dep));
    memset(vis,0,sizeof(vis));

    dep[s]=0;vis[s]=1;

    queue<int>q;q.push(s);
    while(!q.empty()){
        int from=q.front();
        q.pop();
        vis[from]=0;
        for(int i=head[from];i!=-1;i=star[i].next){

            int to=star[i].to;

            if(dep[to]>=dep[from]+1&&star[i].val){//star[i].val!=0
                dep[to]=dep[from]+1;

                if(!vis[to]){
                    q.push(to);
                    vis[to]=1;
                }
            }
        }
    }
    if(dep[t]!=inf)return 1;
    else return 0;

}

int dfs(int from,int flow){

    int rlow=0;

    if(from==t)return flow;

    for(int i=head[from];i!=-1;i=star[i].next){

        int to=star[i].to;

        if(star[i].val&&dep[to]==dep[from]+1){

            if(rlow=dfs(to,min(flow,star[i].val))){
                star[i].val-=rlow;
                star[i^1].val+=rlow;//二进制异或，相同为0，相异为1 
                return rlow;
            }
        }
    }
    return 0;

}

int dinic(){
    int lowflow=0;//当前增广路能通过的最大流量 
    while(bfs()){
        while(lowflow=dfs(s,inf))maxflow+=lowflow;
    }
    return maxflow;
}
int main()
{   
    ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0);
    cin>>n>>m>>s>>t;

    int u,v,w;
    memset(head,-1,sizeof(head));
    for(int i=1;i<=m;i++){
        cin>>u>>v>>w;
        add(u,v,w);
        add(v,u,0);//反向边 
    }
    cout<<dinic();
    return 0;
}