bzoj 3018: [Usaco2012 Nov]Distant Pastures

→题目链接←

跑n*n遍的spfa

每次最后取个max就好

#include<iostream>#include<cstdio>#include<queue>#include<cstring>using namespace std;struct node{int x,y;long long len;};int tox[4]={-1,0,1,0};int toy[4]={0,1,0,-1};int n,A,B;bool a[33][33];long long Min[33][33]; long long ans=0;void shortest_path(int x,int y){for(int i=1; i<=n; i++){for(int j=1; j<=n; j++){Min[i][j]=999999999;}}queue<node>q;node t;t.x=x;t.y=y;t.len=0;Min[x][y]=0;q.push(t);while(!q.empty()){t=q.front();q.pop();for(int i=0; i<4; i++){node t1=t;t1.x+=tox[i];t1.y+=toy[i];if(t1.x<1 || t1.x>n || t1.y<1 || t1.y>n)continue;if(a[t1.x][t1.y]==a[t.x][t.y])t1.len+=A;else t1.len+=B;if(Min[t1.x][t1.y]<=t1.len)continue;Min[t1.x][t1.y]=t1.len;q.push(t1);}}for(int i=1; i<=n; i++){for(int j=1; j<=n; j++){ans=max(Min[i][j],ans);}}}int main(){scanf("%d%d%d\n",&n,&A,&B);for(int i=1; i<=n; i++){for(int j=1; j<=n; j++){char c=getchar();if(c=='(')a[i][j]=0;else a[i][j]=1;}getchar();}for(int i=1; i<=n; i++){for(int j=1; j<=n; j++){shortest_path(i,j);}}printf("%lld\n",ans);return 0;}