hdu3376 Matrix Again

最大费用最大流

咋写？取个相反数就可以了……

#include <iostream>
#include <cstring>
#include <cstdio>
#include <queue>
using namespace std;
int n, a[605][605], ss, tt, hea[750005], cnt, minCost, dis[750005], pre[750005];
queue<int> d;
bool vis[750005];
struct Edge{
	int too, nxt, val, cst;
}edge[2200005];
const int oo=0x3f3f3f3f;
const int dx[]={0, 1, 0};
const int dy[]={0, 0, 1};
int f(int i, int j){
	return (i-1)*n+j;
}
void init(){
	minCost = cnt = 0;
	memset(hea, -1, sizeof(hea));
}
void add_edge(int fro, int too, int val, int cst){
	edge[cnt].nxt = hea[fro];
	edge[cnt].too = too;
	edge[cnt].val = val;
	edge[cnt].cst = cst;
	hea[fro] = cnt++;
}
void addEdge(int fro, int too, int val, int cst){
	add_edge(fro, too, val, cst);
	add_edge(too, fro, 0, -cst);
}
bool spfa(){
	memset(dis, 0x3f, sizeof(dis));
	memset(pre, -1, sizeof(pre));
	d.push(ss);
	vis[ss] = true;
	dis[ss] = 0;
	while(!d.empty()){
		int x=d.front();
		d.pop();
		vis[x] = false;
		for(int i=hea[x]; i!=-1; i=edge[i].nxt){
			int t=edge[i].too;
			if(dis[t]>dis[x]+edge[i].cst && edge[i].val>0){
				dis[t] = dis[x] + edge[i].cst;
				pre[t] = i;
				if(!vis[t]){
					vis[t] = true;
					d.push(t);
				}
			}
		}
	}
	return dis[tt]!=oo;
}
void mcmf(){
	while(spfa()){
		int tmp=0x3f3f3f3f;
		for(int i=pre[tt]; i!=-1; i=pre[edge[i^1].too])
			tmp = min(tmp, edge[i].val);
		for(int i=pre[tt]; i!=-1; i=pre[edge[i^1].too]){
			edge[i].val -= tmp;
			edge[i^1].val += tmp;
			minCost += tmp * edge[i].cst;
		}
	}
}
int main(){
	while(scanf("%d", &n)!=EOF){
		init();
		for(int i=1; i<=n; i++)
			for(int j=1; j<=n; j++)
				scanf("%d", &a[i][j]);
		ss = 0; tt = 2 * n * n + 1;
		addEdge(ss, 1, 2, 0);
		addEdge(1, 1+n*n, 1, 0);
		addEdge(f(n,n), f(n,n)+n*n, 1, 0);
		addEdge(f(n,n)+n*n, tt, 2, 0);
		for(int i=1; i<=n; i++)
			for(int j=1; j<=n; j++){
				addEdge(f(i,j), f(i,j)+n*n, 1, -a[i][j]);
				for(int k=1; k<=2; k++){
					int kx=i+dx[k];
					int ky=j+dy[k];
					if(kx>n || ky>n)	continue;
					addEdge(f(i,j)+n*n, f(kx,ky), oo, 0);
				}
			}
		mcmf();
		printf("%d\n", -minCost);
	}
	return 0;
}