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binary-watch

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:

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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

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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;
}
};
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