Poj 1273 题解

#include<cstdio>
#include<iostream>
#include<cstring>
#include<algorithm>
using namespace std;
struct node
{
int x,y,c,next,other;
}a[6110000]; int len,first[1110000];
int list[1110000],dep[1110000];
int head,tail,n,m;
void ins(int x,int y,int c)
{
int k1,k2;
len++; k1=len;
a[len].x=x; a[len].y=y; a[len].c=c;
a[len].next=first[x]; first[x]=len;

len++; k2=len;
a[len].x=y; a[len].y=x; a[len].c=0;
a[len].next=first[y]; first[y]=len;

a[k1].other=k2;
a[k2].other=k1;
}
void Input()
{
int x,y,c;
memset(first,0,sizeof(first)); len=0;
for(int i=1;i<=m;i++)
{
scanf("%d%d%d",&x,&y,&c);
ins(x,y,c);
}
}
int ans;
bool bfs()
{
memset(dep,0,sizeof(dep));
dep[1]=1; head=1; tail=1; list[1]=1;
while(head<=tail)
{
int x=list[head];
for(int k=first[x];k;k=a[k].next)
{
int y=a[k].y;
if(a[k].c&&dep[y]==0)
{
dep[y]=dep[x]+1;
list[++tail]=y;
}
}
head++;
}
return dep
>0;
}
int dfs(int x,int flow)
{
int delta=0;
if(x==n) return flow;
for(int k=first[x];k;k=a[k].next)
{
int y=a[k].y;
if(dep[y]==dep[x]+1&&a[k].c&&delta<flow)
{
int minf=dfs(y,min(flow-delta,a[k].c));
a[k].c-=minf; a[a[k].other].c+=minf;
delta+=minf;
}
}
if(delta==0) dep[x]=0;
return delta;
}
void Solve()
{
int delta; ans=0;
while(bfs())
{
while(delta=dfs(1,0x3fffffff)) ans+=delta;
}
}
void Output()
{
printf("%d\n",ans);
}
int main()
{
freopen("a.in","r",stdin);
freopen("a.out","w",stdout);
while(scanf("%d%d",&m,&n)!=EOF)
{
Input();
Solve();
Output();
}
}