【BZOJ】【P1324】【Exca王者之剑】【题解】【最小割】

传送门:http://www.lydsy.com/JudgeOnline/problem.php?id=1324

其实题目就是给定n*m棋盘，不能取相邻的格子,最大收益,裸的最小割

Code:

#include<cstdio>
#include<iostream>
#include<algorithm>
#include<cstring>
#include<vector>
#include<climits>
#include<queue>
using namespace std;
const int maxn=20010;
struct edge{
	int u,v,cap,flow;	
	edge(int _u=0,int _v=0,int _cap=0,int _flow=0):
		u(_u),v(_v),cap(_cap),flow(_flow){}
};
vector<edge>edges;
vector<int>G[maxn];
int cur[maxn],vis[maxn];
void add(int u,int v,int cap){
	edges.push_back(edge(u,v,cap,0));
	G[u].push_back(edges.size()-1);
	edges.push_back(edge(v,u,0,0));	
	G[v].push_back(edges.size()-1);	
}
int d[maxn],s,t;
bool bfs(){
	memset(vis,0,sizeof(vis));
	queue<int>q;
	q.push(s);vis[s]=1;
	while(!q.empty()){
		int u=q.front();q.pop();
		for(int i=0;i<G[u].size();i++){
			edge e=edges[G[u][i]];
			if(e.cap>e.flow&&!vis[e.v]){
				d[e.v]=d[u]+1;
				vis[e.v]=1;
				q.push(e.v);
			}
		}
	}return vis[t];
}
int dfs(int u,int a){
	int flow=0,f;
	if(u==t||!a)return a;
	for(int &i=cur[u];i<G[u].size();i++){
		edge e=edges[G[u][i]];
		if(d[e.v]==d[u]+1&&(f=dfs(e.v,min(a,e.cap-e.flow)))>0){
			edges[G[u][i]].flow+=f;
			edges[G[u][i]^1].flow-=f;
			flow+=f;
			a-=f;
			if(!a)break;
		}
	}return flow;
}
int Dinic(){
	int flow=0;
	while(bfs()){
		int x=0;
		do{
			flow+=x;
			memset(cur,0,sizeof(cur));
		}while(x=dfs(s,INT_MAX));
	}return flow;
}
int n,tot,m;
int hash[201][201];
int a[201][201];
int sum=0;
const int dx[4]={0,1,0,-1};
const int dy[4]={1,0,-1,0};
int main(){
	cin>>n>>m;
	for(int i=1;i<=n;i++)
	for(int j=1;j<=m;j++){
		cin>>a[i][j];
		hash[i][j]=++tot;
		sum+=a[i][j];
	}
	s=0;t=tot+1;
	for(int i=1;i<=n;i++)
	for(int j=1;j<=m;j++){
		if((i+j+1)&1)
			add(s,hash[i][j],a[i][j]);
		else
			add(hash[i][j],t,a[i][j]);
		if((i+j+1)&1)
		for(int k=0;k<4;k++){
			int x=i+dx[k],y=j+dy[k];
			if(x<1||x>n||y<1||y>m)continue;
			add(hash[i][j],hash[x][y],INT_MAX);
		}
	}
	int deb=0;
	if(deb)
	for(int i=0;i<edges.size();i++){
		edge e=edges[i];
		if(i%2==0)
		printf("%d -> %d cap:%d\n",e.u,e.v,e.cap);
	}
	cout<<sum-Dinic()<<endl;
	return 0;	
}