51nod

并查集随便搞一下就过了。
 1 #include <bits/stdc++.h>
 2 using namespace std;
 3 const int maxn = 2505;
 4 int n, m;
 5 int fa[maxn];
 6 char s[55][55];
 7 //int dx[]={1, 1, 0, 0}
 8 int ety(int x, int y) {
 9     return x*m+y;
10 }
11 void init(int n) {
12     for(int i=0; i<=n; i++) {
13         fa[i] = i;
14     }
15 }
16 int get(int x) {
17     return fa[x] == x ? x : fa[x] = get(fa[x]);
18 }
19 bool join(int x, int y) {
20     int rx = get(x), ry = get(y);
21     if(rx == ry) return false;
22     fa[rx] = fa[ry] = min(rx, ry);
23     return true;
24 }
25 int main() {
26 
27     while(~scanf("%d%d", &n, &m)) {
28         getchar();
29         for(int i=0; i<n; i++) {
30             gets(s[i]);
31         }
32         init(n*m);
33         bool ok = true;
34         for(int i=0; i<n; i++) {
35             for(int j=0; j<m; j++) {
36                 if(i!=n-1 && s[i][j] == s[i+1][j]) ok = join(ety(i, j), ety(i+1, j));
37                 if(!ok) break;
38                 if(j!=m-1 && s[i][j] == s[i][j+1]) ok = join(ety(i, j), ety(i, j+1));
39                 if(!ok) break;
40             }
41             if(!ok) break;
42         }
43         if(ok) printf("No
");
44         else printf("Yes
");
45     }
46     return 0;
47 }