剑指 Offer 13. 机器人的运动范围

DFS。

class Solution {
public:
    int n, m;

    int single_sum(int x) {
        int res = 0;
        while (x) {
            res += x % 10;
            x /= 10;
        }
        return res;
    }

    int sum(int x, int y) {
        return single_sum(x) + single_sum(y);
    }

    bool check(int x, int y) {
        return x >= 0 && x < n && y >=0 && y < m;
    }

    int dfs(int x, int y, int k, vector<vector<bool>> &vis) {
        if (sum(x, y) > k) return 0;
        vis[x][y] = true;
        int res = 1;
        int dx[] = {-1, 0 ,1, 0}, dy[] = {0, 1, 0, -1};
        for (int i = 0; i < 4; i++) {
            int a = x + dx[i], b = y + dy[i];
            if (check(a, b) && !vis[a][b])
                res += dfs(a, b, k, vis);
        }
        return res;
    }

    int movingCount(int n, int m, int k) {
        this->n = n, this->m = m;
        vector<vector<bool>> vis(n, vector<bool>(m));
        return dfs(0, 0, k, vis);
    }
};