1 #include <cstdio> 2 #include <cstring> 3  4 #define MAXN 105 5  6 char map[MAXN][MAXN]; 7 char visit[27]; 8 int n, m; 9 10 bool check(char c) {11     int i, j;12     int x1=MAXN, y1=MAXN, x2=-1, y2=-1;13 14     for (i=0; i<n; ++i) {15         for (j=0; j<m; ++j) {16             if (map[i][j] == c) {17                 if (i<x1)   x1 = i;18                 if (j<y1)   y1 = j;19                 if (i>x2)   x2 = i;20                 if (j>y2)   y2 = j;21             }22         }23     }24     if (x2-x1<2 || y2-y1<2)25         return false;26     for (i=x1; i<=x2; ++i)27         if (map[i][y1]!=c || map[i][y2]!=c)28             return false;29     for (j=y1; j<=y2; ++j)30         if (map[x1][j]!=c || map[x2][j]!=c)31             return false;32     for (i=x1+1; i<x2; ++i)33         for (j=y1+1; j<y2; ++j)34             if (map[i][j] != ‘.‘)35                 return false;36     return true;37 }38 39 int main() {40     int i;41     int j;42 43     while (scanf("%d %d", &n, &m)!=EOF && (n||m)) {44         memset(visit, false, sizeof(visit));45         for (i=0; i<n; ++i) {46             scanf("%s", map[i]);47             for (j=0; j<m; ++j) {48                 if (map[i][j] != ‘.‘) {49                     visit[map[i][j]-‘A‘] = true;50                 }51             }52         }53         for (i=0; i<26; ++i) {54             if (visit[i] && check(i+‘A‘))55                 printf("%c", i+‘A‘);56         }57         printf("\n");58     }59 60     return 0;61 }