bzoj 1661: [Usaco2006 Nov]Big Square 巨大正方形 （枚举）

题目描述

传送门

题解

枚举矩形的两个端点（同一条边上的），然后求出剩下的两个端点，判断是否合法，并更新答案。

代码

#include<iostream>#include<cstdio>#include<algorithm>#include<cstring>#define N 103using namespace std;int cnt,n;int mp[N][N];struct data{    int x,y;}a[N*N];int cmp(data a,data b){    return a.x<b.x||a.x==b.x&&a.y<b.y;}int pow(int x){    return x*x;}int main(){    scanf("%d",&n);    for (int i=1;i<=n;i++){        char s[N]; scanf("%s",s+1);        for (int j=1;j<=n;j++) {            if (s[j]=='B') mp[i][j]=-1;            if (s[j]=='J') a[++cnt].x=i,a[cnt].y=j,mp[i][j]=1;        }    }    int ans=0;    for (int x1=1;x1<=n;x1++)     for (int y1=1;y1<=n;y1++)      for (int x2=x1+1;x2<=n;x2++)       for (int y2=1;y2<=y1;y2++)       {         if (mp[x1][y1]==-1||mp[x2][y2]==-1) continue;         int cnt=0;         int len1=abs(x1-x2); int len2=abs(y1-y2);         int x3=x1+len2; int y3=y1+len1;         int x4=x2+len2; int y4=y2+len1;         if (x3<1||y3<1||x3>n||y3>n) continue;         if (x4<1||y4<1||x4>n||y4>n) continue;         if (mp[x4][y4]==-1||mp[x3][y3]==-1) continue;         cnt=mp[x1][y1]+mp[x2][y2]+mp[x3][y3]+mp[x4][y4];         if (cnt<3) continue;         ans=max(ans,pow(len1)+pow(len2));      }    printf("%d\n",ans);}