401. Binary Watch（LeetCode）

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".

不得不說下面的方法實在是好，思路很清晰，這個不是我作的，拿過來，你們看看，學習學習

 1 class Solution {
 2 public:
 3     vector<string> readBinaryWatch(int num) {
 4          vector<string> rs;
 5     for (int h = 0; h < 12; h++)
 6     for (int m = 0; m < 60; m++)
 7         if (bitset<10>(h << 6 | m).count() == num)
 8             rs.emplace_back(to_string(h) + (m < 10 ? ":0" : ":") + to_string(m));
 9     return rs;
10     }
11 };