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#include <stdio.h>
#include <queue>
using namespace std;
struct INFO{
int y;
int x;
int py;
int px;
};
char buf[50][51];
bool visit[50][50];
int dx[4] = {0,1,0,-1};
int dy[4] = {-1,0,1,0};
int N, M;
bool BFS(){
for(int i = 0; i < N; ++i)
for(int j = 0; j < M; ++j){
if(!visit[i][j]){
queue<INFO> q;
INFO info;
q.push({i,j,i,j});
visit[i][j] = true;
while(!q.empty()){
info = q.front();
q.pop();
for(int k=0; k<4; ++k){
int ny = info.y + dy[k];
int nx = info.x + dx[k];
if(0<=nx&&nx<M && 0<=ny&&ny<N && !(ny==info.py && nx==info.px) && buf[ny][nx]==buf[info.y][info.x]){
if(visit[ny][nx]) return true;
visit[ny][nx] = true;
q.push({ny,nx,info.y,info.x});
}
}
}
}
}
return false;
}
int main(){
scanf("%d %d",&N,&M);
for(int i = 0; i < N; ++i)
scanf("%s",buf[i]);
BFS() ? printf("Yes") : printf("No");
}
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