BZOJ 大视野 1001 狼抓兔子 解题报告

#include<cstdio>
#include<cstring>
#include<iostream>
using namespace std;
struct node
{
int x,y,c,next,other;
}a[6110000]; int len,first[1110000];
int list[1110000],h[1110000];
int st,ed,head,tail,n,m;

void ins( int x,int y,int c )
{
int k1,k2;
k1=++len;
k2=++len;
a[k1].x=x; a[k1].y=y; a[k1].c=c;
a[k2].x=y; a[k2].y=x; a[k2].c=c;
a[k1].next = first[x]; first[x] = k1;
a[k2].next = first[y]; first[y] = k2;

a[k1].other = k2;
a[k2].other = k1;
}
bool bfs()
{
memset( h,0,sizeof h );
memset( list,0,sizeof list );
h[st]=1; list[1]=st;
head=tail=1;
while( head<=tail )
{
int x=list[head];
for( int k=first[x];k;k=a[k].next )
{
int y=a[k].y;
if( !h[y] && a[k].c )
{
h[y] = h[x]+1;
list[ ++tail ] = y;
}
}
head++;
}
return h[ed]>0;
}
int dfs( int x,int flow )
{
if( x==ed ) return flow;
int delta=0,y,p;
for( int k=first[x];k;k=a[k].next )
{
int y=a[k].y;
if( h[y] == h[x]+1 && a[k].c && delta<flow )
{
p=dfs( y,min( flow-delta,a[k].c ) );
delta+=p;
a[k].c-=p; a[ a[k].other ].c+=p;
}
}
if( delta == 0 )h[x] = 0;
return delta;
}

int main()
{
memset( first,0,sizeof first ); len = 0;
int i,j,x,k,delta;

scanf( "%d%d",&n,&m );
st = 1; ed = n*m;
for( i=1;i<=n;i++ )
for( j=1;j<m;j++ )
{
scanf( "%d",&x );
k = (i-1)*m+j;
ins( k,k+1,x );
}
for( i=1;i<n;i++ )
for( j=1;j<=m;j++ )
{
scanf("%d",&x);
k = (i-1)*m+j;
ins( k,k+m,x );
}
for( i=1;i<n;i++ )
for( j=1;j<m;j++ )
{
scanf("%d",&x);
k = (i-1)*m+j;
ins( k,k+m+1,x );
}
k=0;
while( bfs() )
{
while( delta=dfs( st,0x7fffffff ) ) k+=delta;
}
printf("%d\n",k);

return 0;
}