http://codeforces.com/problemset/problem/510/B
#include "cstdio" #include "cstring" int r,c; char map[55][55]; int vis[55][55]; int mark; int dx[4]={1,-1,0,0},dy[4]={0,0,1,-1}; int judge(int x,int y) { if(x<0||x>=r||y<0||y>=c) return 0; return 1; } void dfs(int x,int y,int perX,int perY) { if(!judge(x,y)) return; vis[x][y]=1; for(int i=0;i<4;i++) { int xx=x+dx[i]; int yy=y+dy[i]; if(map[xx][yy]==map[x][y]&&judge(xx,yy)&&(xx!=perX||yy!=perY)) { if(vis[xx][yy]) { mark=1; return; } dfs(xx,yy,x,y); } } return; } int main() { while(scanf("%d%d",&r,&c)!=EOF) { memset(vis,0,sizeof(vis)); for(int i=0;i<r;i++) scanf("%s",map[i]); mark=0; int flag=1; for(int i=0;i<r;i++) { for(int j=0;j<c;j++) { if(!vis[i][j]) { dfs(i,j,0,0); if(mark) { break; } } } if(mark) { break; } } if(mark) printf("Yes "); else printf("No "); } return 0; }