题目链接

Red and Black POJ - 1979

思路

dfs，注意行列！

时间复杂度

$$ 每组O(NM) $$

代码

#include <cstdio>
using namespace std;

const int MAXN = 25;

char s[MAXN][MAXN];

int n, m;
int ans;

int dx[] = {0, 0, 1, -1};
int dy[] = {1, -1, 0, 0};

bool check(int x, int y) {
    if (1 <= x && x <= n && 1 <= y && y <= m && s[x][y] == '.') {
        return true;
    } else {
        return false;
    }
}

void dfs(int x, int y) {
    s[x][y] = '#';
    ans++;
    for (int i = 0; i < 4; i++) {
        int xx = x + dx[i];
        int yy = y + dy[i];
        if (check(xx, yy)) {
            dfs(xx, yy);
        }
    }
}

int main() {
    while (scanf("%d%d", &m, &n), n + m){
        for (int i = 1; i <= n; i++) {
            scanf("%s", s[i] + 1);// no &
        }
        ans = 0;
        for (int i = 1; i <= n; i++) {
            for (int j = 1; j <= m; j++) {
                if (s[i][j] == '@') {
                    dfs(i, j);
                }
            }
        }
        printf("%d\n", ans);
    }
    return 0;
}