SAP解决USACO4.2.1网络流问题

/*
ID: hk945801
TASK: ditch
LANG: C++
*/
#include<iostream>
#include<cstdio>
#include<cstring>
using namespace std;
int a[201][201],pre[201],level[201],gap[201];
int main(){
int i,j,k,m,n;
freopen("ditch.in","r",stdin);
freopen("ditch.out","w",stdout);
cin>>m>>n;
for(i=1;i<=m;i++){
int x,y,z;
cin>>x>>y>>z;
a[x][y]+=z;
}
int s=1;
gap[0]=n;
int v,p=pre[s]=s;
int ans=0,sum;
while(level[s]<n){
for(v=1;v<=n;v++){
if(a[p][v]>0 && level[p]==level[v]+1){
break;
}
}
if(v<=n){
pre[v]=p;
p=v;
if(v==n){
sum=1000000001;
for(i=v;i!=s;i=pre[i]){
if(sum>a[pre[i]][i])sum=a[pre[i]][i];
}
ans+=sum;
for(i=v;i!=s;i=pre[i]){
a[pre[i]][i]-=sum;
a[i][pre[i]]+=sum;
}
p=s;
}
}else {
int min=n;
for(v=1;v<=n;v++){
if(a[p][v]>0 && min>level[v]){
min=level[v];
}
}
gap[level[p]]--;
if(gap[level[p]]==0)break;
level[p]=min+1;
gap[level[p]]++;
p=pre[p];
}
}
cout<<ans<<endl;
return 0;
}