hdu 1565 网络流（EK算法）

#include <cstdio>
#include <iostream>
#include <cstring>
#include <queue>


using namespace std;
#define INF 0x3fffffff
int v[4][2] = {{1,0},{0,1},{-1,0},{0,-1}};

int ma[500][500];
int a[500][500];
int flow[505][505];
int p[500];
int n;
int maxflow(int s,int t){
	queue<int> q;
	memset(flow,0,sizeof(flow));
	int f = 0;
	int d[500];
	while(1){
		memset(d,0,sizeof(d));
		d[s] = INF;
		q.push(s);
		while(!q.empty()){
			int u = q.front();
			q.pop();
			      
			for(int v = 0; v <= n*n+1; v++){
				if(!d[v] && ma[u][v] > flow[u][v]){
					p[v] = u;
					q.push(v);
					d[v] = min(d[u],ma[u][v] - flow[u][v]);
				}
			}
		}
		if(d[t] == 0) break;
		for(int u  = t; u != s; u = p[u]){
			flow[p[u]][u] += d[t];
			flow[u][p[u]] -= d[t];			
		}
		f += d[t];
	}	
	return f;
}

int main(){
	while(cin >> n){
		int sum  = 0;
		memset(ma,0,sizeof(ma));
		
		for(int i = 1;i <= n;i++){
			for(int j = 1;j <= n;j++){
				cin >> a[i][j];
				sum += a[i][j];	
			}
		}
		
		for(int i = 1;i <= n;i++){
			for(int j = 1;j <= n;j++){
				if((i+j)%2 == 0){
					ma[0][(i-1)*n+j] = a[i][j];
				}
				else{
					ma[(i-1)*n+j][n*n+1] = a[i][j];
				}
			}
		}
		
		
		for(int i = 1;i <= n;i++){
			for(int j = 1;j <= n;j++){
				for(int k = 0;k < 4;k++){
					int x = i + v[k][0];
					int y = j + v[k][1];
					
					if(x>0 && x <= n && y > 0 && y<=n && (i+j)%2 == 0){
						ma[(i-1)*n + j] [(x-1)*n + y] = INF;
 					}
				}
			}
		}
		
		cout <<sum - maxflow(0,n*n+1)<< endl;
	}
	return 0;
}
定理：
最小割=最大流=最小点权覆盖集=sum - 最大独立点集

hdu 1565 网络流（EK算法）

原文：http://blog.csdn.net/qq_24667639/article/details/46925233