Description
It‘s election time. The farm is partitioned into a 5x5 grid of cow locations, each of which holds either a Holstein (‘H‘) or Jersey (‘J‘) cow. The Jerseys want to create a voting district of 7 contiguous (vertically or horizontally) cow locations such that the Jerseys outnumber the Holsteins. How many ways can this be done for the supplied grid?
农场被划分为5x5的格子,每个格子中都有一头奶牛,并且只有荷斯坦(标记为H)和杰尔西(标记为J)两个品种.如果一头奶牛在另一头上下左右四个格子中的任一格里,我们说它们相连. 奶牛要大选了.现在有一只杰尔西奶牛们想选择7头相连的奶牛,划成一个竞选区,使得其中它们品种的奶牛比荷斯坦的多. 要求你编写一个程序求出方案总数.
Input
* Lines 1..5: Each of the five lines contains five characters per line, each ‘H‘ or ‘J‘. No spaces are present.
5行,输入农场的情况.
Output
* Line 1: The number of distinct districts of 7 connected cows such that the Jerseys outnumber the Holsteins in the district.
输出划区方案总数.
Sample Input
HHHHH
JHJHJ
HHHHH
HJHHJ
HHHHH
Sample Output
2
HINT
usaco良心网站,直接暴力不会挂……233
暴力枚举点就行了,每次枚举就在已经选到的点周围选就行咯,随手带几个剪枝。
至于去重,直接hash就好。在累计答案处hash:64MS,每一层搜索都hash(去掉重复扩展的状态)20MS,玩火人工二分MOD:44MS、48MS……
运气#1
#include<cstdio> #include<cstring> #include<algorithm> using namespace std; const int MOD=10001; int ans=0,xx,yy,k; int hash[MOD]; char c[5][5]; void dfs(int x,int y,int hn,int jn,int p){ if (x<0||y<0||x>4||y>4) return; if (x<xx||(x==xx&&y<yy)) return; if (c[x][y]==‘H‘) hn++;else jn++; if (hn>3) return; p+=1<<((x*5+y)); k=p%MOD; while(hash[k]!=-1){ if (hash[k]==p) return; k++; if (k>=MOD) k-=MOD; } hash[k]=p; if (hn+jn==7){ ans++; return; } char s=c[x][y]; c[x][y]=0; for (int i=0;i<5;i++) for (int j=0;j<5;j++) if (c[i][j]==0){ if (c[i+1][j]!=0) dfs(i+1,j,hn,jn,p); if (c[i-1][j]!=0) dfs(i-1,j,hn,jn,p); if (c[i][j+1]!=0) dfs(i,j+1,hn,jn,p); if (c[i][j-1]!=0) dfs(i,j-1,hn,jn,p); } c[x][y]=s; } int main(){ for (int i=0;i<5;i++) scanf("%s",c[i]); memset(hash,-1,sizeof(hash)); for (xx=0;xx<5;xx++) for (yy=0;yy<5;yy++) dfs(xx,yy,0,0,0); printf("%d\n",ans); }