POJ 1979 Red and Black

#include <iostream>
#include <cstdio>
#include <cstring>
#define REP(i, s, n) for(int i = s; i <= n; i ++)
#define REP_(i, s, n) for(int i = n; i >= s; i --)
#define MAX_N 20 + 5

using namespace std;

int n, m, ans = 0;
bool map[MAX_N][MAX_N], used[MAX_N][MAX_N];
char ch;
int dx[5] = {0, -1, 0, 0, 1}, dy[5] = {0, 0, -1, 1, 0};

void dfs(int s, int t){
    if(map[s][t]) ans ++;
    REP(i, 1, 4){
        int ns = s + dx[i], nt = t + dy[i];
        if(ns >= 1 && ns <= m && nt >= 1 && nt <= n && map[ns][nt] && !used[ns][nt]){
            used[ns][nt] = 1; dfs(ns, nt); 
        }
    }
}
            
int main(){
    while(scanf("%d%d", &n, &m) != EOF){
        if(n == 0 && m == 0) break;
        memset(used, 0, sizeof(used));
        int s, t; ans = 0; getchar();
        REP(i, 1, m){
            REP(j, 1, n){ 
                cin >> ch;
                if(ch == ‘@‘) {s = i, t = j; map[i][j] = 1; continue;}
                map[i][j] = (ch == ‘.‘ ? 1 : 0);
            }
            getchar();
        }
        
        used[s][t] = 1;
        dfs(s, t);
        printf("%d\n", ans);
    }
    return 0;
}