学步园

因为要字典序最小，直接从第一个开始求答案即可

AC代码如下：

#include <iostream>
#include <cstring>
#include <cstdio>
#include <algorithm>
using namespace std;

char s[15][15];
int n;

bool judge( int x, int y, int k ){
    return k != s[x][y+1] && k != s[x][y-1] && k != s[x+1][y] && k != s[x-1][y];
}

int main(){
    int T, Case = 1;
    cin >> T;
    while( T-- ){
        cin >> n;
        for( int i = 0; i <= n + 1; i++ ){
            for( int j = 0; j <= n + 1; j++ ){
                s[i][j] = '.';
            }
        }
        for( int i = 1; i <= n; i++ ){
            scanf( "%s", &s[i][1] );
        }
        for( int i = 1; i <= n; i++ ){
            for( int j = 1; j <= n; j++ ){
                if( s[i][j] != '.' )    continue;
                for( int k = 'A'; k <= 'Z'; k++ ){
                    if( judge( i, j, k ) ){
                        s[i][j] = k;
                        break;
                    }
                }
            }
        }
        printf( "Case %d:\n", Case++ );
        for( int i = 1; i <= n; i++ ){
            for( int j = 1; j <= n; j++ ){
                printf( "%c", s[i][j] );
            }
            cout << endl;
        }
    }
    return 0;
}