USACO 4.2.1 网络流 Dinic

/*
ID: shenxyy1
PROG: ditch
LANG: C++
*/
#include<stdio.h>
#include<stdlib.h>
#include<string.h>
#include<iostream>
#include<algorithm>
#define max(x,y) ((x)>(y)?(x):(y))
#define min(x,y) ((x)<(y)?(x):(y))
#define For(i,j,k) for (i=j;i<=k;i++)
using namespace std;

const int dmax=1010,INF=1000000000;
int a[dmax][dmax],q[dmax*dmax],d[dmax*dmax],m,n;

bool bfs(){
int f=0,l=1,i,j,k;
memset(d,-1,sizeof(d));
q[1]=1;
d[1]=0;
while (f<l){
k=q[++f];
For(i,1,n)
if (d[i]==-1 && a[k][i]>0){
d[i]=d[k]+1;
q[++l]=i;
}
}
return d
>0;
}
int dfs(int x,int low){
int i,k;
if (x==n) return low;
For(i,1,n)
if (d[x]+1==d[i] && a[x][i]>0 && (k=dfs(i,min(low,a[x][i])))){
a[x][i]-=k;
a[i][x]+=k;
return k;
}
return 0;
}

int main(){
int i,j,k,x,y,z;
freopen("ditch.in","r",stdin);
freopen("ditch.out","w",stdout);
scanf("%d%d",&m,&n);
for (i=1;i<=m;i++){
scanf("%d%d%d",&x,&y,&z);
a[x][y]+=z;
}
int ans=0;
while (bfs()){
while (k=dfs(1,INF)) ans+=k;
}
printf("%d\n",ans);
return 0;
}