73分求助

#include<iostream>
#include<cstdio>
#include<algorithm>
#include<cstring>
#include<queue>
#define ll long long
#define re register
#define in inline
using namespace std;
const ll inf=2147483647;
in ll read()
{
	ll x=0,k=1;
	char c=getchar();
	while(!isdigit(c))
	{
		if(c=='-') k=-1;
		c=getchar();
	}
	while(isdigit(c))
	{
		x=(x<<1)+(x<<3)+(c^48);
		c=getchar();
	}
	return x*k;
}
ll z,ans;
int n,m,s,t;
int x,y;
struct eg{
	int v,nxt;
	ll w;
}edge[10001];
int head[5001],dis[5001],cnt=1,now[5001];
in void build(int u,int v,ll w)
{
	edge[++cnt].v=v;
	edge[cnt].w=w;
	edge[cnt].nxt=head[u];
	head[u]=cnt;
	
	edge[++cnt].v=u;
	edge[cnt].w=0;
	edge[cnt].nxt=head[v];
	head[v]=cnt;
}	
in int bfs()
{
	for(re int i=1;i<=n;++i)
	{
		dis[i]=inf;
	}
	queue<int> q;
	q.push(s);
	dis[s]=0;
	now[s]=head[s];
	while(!q.empty())
	{
		int u=q.front();
		q.pop();
		for(re int i=head[u];i!=0;i=edge[i].nxt)
		{
			int v=edge[i].v;
			if(edge[i].w>0 and dis[v]==inf)
			{
				dis[v]=dis[u]+1;
				q.push(v);
				now[v]=head[v];
				if(v==t) return 1;
			}
		}
	}
	return 0;
}
in ll dfs(int x,ll left)
{
	if(x==t) return left;
	ll k,out=0;
	for(re int i=now[x];i!=0 and left!=0;i=edge[i].nxt)
	{
		int v=edge[i].v;
		if(edge[i].w>0 and dis[v]==dis[x]+1)
		{
			k=dfs(v,min(left,edge[i].w));
			if(k==0) dis[v]=inf;
			left-=k,out+=k;
			edge[i].w-=k,edge[i^1].w+=k;
		}
	}
	return out;
}
in void dinic()
{
	while(bfs())
	{
		ans+=dfs(s,inf);
	}
}
int main()
{
	n=read(),m=read(),s=read(),t=read();
	for(re int i=1;i<=m;++i)
	{
		x=read(),y=read(),z=read();
		build(x,y,z);
	}
	dinic();
	printf("%lld",ans);
	return 0;
}