401. Binary Watch

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".

Rust Solution

struct Solution;

impl Solution {
    fn read_binary_watch(num: i32) -> Vec<String> {
        let mut res: Vec<String> = vec![];
        for i in 0..11 {
            for j in 0..60 {
                if i32::count_ones(i) + i32::count_ones(j) == num as u32 {
                    res.push(format!("{}:{:02}", i, j));
                }
            }
        }
        res
    }
}

#[test]
fn test() {
    let num = 1;
    let mut res: Vec<String> =
        vec_string!["1:00", "2:00", "4:00", "8:00", "0:01", "0:02", "0:04", "0:08", "0:16", "0:32"];
    res.sort_unstable();
    assert_eq!(Solution::read_binary_watch(num), res);
}

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