LeetCode每日一题：1601. 最多可达成的换楼请求数目

1601. 最多可达成的换楼请求数目

二进制枚举、模拟

class Solution {
public:
    vector<vector<int>> re;
    int ans = 0, m;
    int sum[21];

    int lowbit(int i) {
        return i & (-i);
    }
    int get(int u) {
        int res = 0;
        while (u) {
            u -= lowbit(u);
            res ++ ;
        }
        return res;
    }

    bool check(int u) {
        memset(sum, 0, sizeof sum);
        int res = 0;
        for (int i = 0; i < m; i ++ )
            if (u >> i & 1) {
                int a = re[i][0], b = re[i][1];
                if (++sum[a] == 1) res ++ ;
                if (--sum[b] == 0) res -- ;
            }
        return res == 0;
    }
    int maximumRequests(int n, vector<vector<int>>& requests) {
        re = requests;
        m = re.size();
        for (int i = 0; i < 1 << m; i ++ ) {
            int cnt = get(i);
            if (cnt < ans) continue;
            if (check(i)) ans = cnt;
        }
        return ans;
    }
};