HDU 1532 Drainage Ditches(Dinic)

#include <iostream>
#include <algorithm>
#include <cstdio>
#include <cstring>
#include <cstdlib>
#include <queue>
#include<math.h>
#define inf 0x3f3f3f3f
#define ls l,mid,rt<<1
#define rs mid+1,r,rt<<1|1
#define maxn 10000000

using namespace std;

struct node
{
int to,w,next;
} q[300000];
int head[300000],l[300000],cnt,s,e;
void bu(int a,int b,int c)
{
q[cnt].to=b;
q[cnt].w=c;
q[cnt].next=head[a];
head[a]=cnt++;

q[cnt].to=a;
q[cnt].next=head[b];
q[cnt].w=0;
head[b]=cnt++;
}
int bfs()
{
queue<int >Q;
while(!Q.empty())
Q.pop();
memset(l,-1,sizeof(l));
l[s]=0;
Q.push(s);
while(!Q.empty())
{
int v=Q.front();
Q.pop();
for(int i=head[v]; ~i; i=q[i].next)
{
if(q[i].w>0&&l[q[i].to ]==-1)
{
l[q[i].to ]=l[v]+1;
Q.push(q[i].to);
}
}
}
return l[e]!=-1;
}
int dfs(int x,int f)
{
if(x==e)
{
return f;
}
int tmp=0,a;
for(int i=head[x]; ~i; i=q[i].next)
{
if(q[i].w>0&&(l[q[i].to ]==l[x]+1 ))
{
if(a=dfs(q[i].to,min(q[i].w,f-tmp)))
{
q[i].w-=a;
q[i^1].w+=a;
tmp+=a;
}
}
}
if(tmp==0)
l[x]=-1;
return tmp;
}
int main()
{
int n,m,i,j,k,cla,A=1;
while(~scanf("%d%d",&m,&n))
{
int a,b,c;
cnt=0;
s=1,e=n;
memset(head,-1,sizeof(head));
for(i=0; i<m; i++)
{
scanf("%d%d%d",&a,&b,&c);
bu(a,b,c);
}
int ans=0;
while(bfs())
{
ans+=dfs(1,inf);
}
printf("%d\n",ans);
}
return 0;
}