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# binary-watch

发表于 2016-09-29 更新于 2020-01-12 分类于 leetcode 阅读次数： 阅读次数： Disqus：

### problem

A binary watch has 4 LEDs on the top which represent the hours (0-11), and the 6 LEDs on the bottom represent the minutes (0-59).

Each LED represents a zero or one, with the least significant bit on the right.

For example, the above binary watch reads “3:25”.

Given a non-negative integer n which represents the number of LEDs that are currently on, return all possible times the watch could represent.

#### Example:

    Input: n = 1
    Return: ["1:00", "2:00", "4:00", "8:00", "0:01", "0:02", "0:04", "0:08", "0:16", "0:32"]

#### Note:

- The order of output does not matter.
- The hour must not contain a leading zero, for example “01:00” is not valid, it should be “1:00”.
- The minute must be consist of two digits and may contain a leading zero, for example “10:2” is not valid, it should be “10:02”.

### 题解

又是参（chao）考（xi）别人的代码，嗯，就是这么不要脸，链接

#### Code

    class Solution {
    public:
        vector<string> readBinaryWatch(int num) {
            vector<string> res;
            for (int h = 0; h < 12; ++h) {
                for (int m = 0; m < 60; ++m) {
                    if (bitset<10>((h << 6) + m).count() == num) {
                        res.push_back(to_string(h) + (m < 10 ? ":0" : ":") + to_string(m));
                    }
                }
            }
            return res;
        }
    };