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;

}
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hdu3376 Matrix Again

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