UVa 10946 Do You What Filled? (DFS)

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

const int N = 55;
int n, m, id;
char g[N][N];
bool vis[N][N];
struct node {
    char x;
    int num;
}ans[3000];
void dfs( int u, int v ) {
    vis[u][v] = true;
    ans[id].num++;
    if ( u > 0 && g[u][v] == g[u-1][v] && !vis[u-1][v] ) dfs( u-1, v );
    if ( u < n-1 && g[u][v] == g[u+1][v] && !vis[u+1][v] ) dfs( u+1, v);
    if ( v > 0 && g[u][v-1] == g[u][v] && !vis[u][v-1] ) dfs( u, v-1 );
    if ( v < m-1 && g[u][v] == g[u][v+1] && !vis[u][v+1] ) dfs( u, v+1 );
}
bool cmp ( node a, node b ) { 
    if ( a.num == b.num ) return a.x < b.x;
    return a.num > b.num; 
}
int main()
{
    int pro = 1;
    while ( scanf("%d%d", &n, &m) != EOF && !( !m && !n ) ) {
        id = 0;
        getchar();
        for ( int i = 0; i < n; getchar(), ++i )
            for ( int j = 0; j < m; ++j ) scanf("%c", &g[i][j]);
        memset( vis, 0, sizeof(vis));
        for ( int i = 0; i < n; ++i )
            for ( int j = 0; j < m; ++j ) 
                if ( g[i][j] != '.' && !vis[i][j] ) {
                    ans[id].x = g[i][j];
                    ans[id].num = 0;
                    dfs( i, j ); id++;
                }
        sort( ans, ans + id, cmp );
        printf("Problem %d:
", pro++);
        for ( int i = 0; i < id; ++i ) printf("%c %d
", ans[i].x, ans[i].num);
    }
}