main.cpp

// Source: https://leetcode.com/problems/binary-watch
// Title: Binary Watch
// Difficulty: Easy
// Author: Mu Yang <http://muyang.pro>

////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
// A binary watch has 4 LEDs on the top to represent the hours (0-11), and 6 LEDs on the bottom to representthe minutes (0-59). Each LED represents a zero or one, with the least significant bit on the right.
//
// - For example, the below binary watch reads `"4:51"`.
//
// https://assets.leetcode.com/uploads/2021/04/08/binarywatch.jpg
//
// Given an integer `turnedOn` which represents the number of LEDs that are currently on (ignoring the PM), return all possible times the watch could represent. You may return the answer in **any order**.
//
// The hour must not contain a leading zero.
//
// - For example, `"01:00"` is not valid. It should be `"1:00"`.
//
// The minute mustconsist of two digits and may contain a leading zero.
//
// - For example, `"10:2"` is not valid. It should be `"10:02"`.
//
// **Example 1:**
//
// ```
// Input: turnedOn = 1
// Output: ["0:01","0:02","0:04","0:08","0:16","0:32","1:00","2:00","4:00","8:00"]
// ```
//
// **Example 2:**
//
// ```
// Input: turnedOn = 9
// Output: []
// ```
//
// **Constraints:**
//
// - `0 <= turnedOn <= 10`
//
////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////

#include <bit>
#include <format>
#include <string>
#include <vector>

using namespace std;

class Solution {
 public:
  vector<string> readBinaryWatch(int turnedOn) {
    auto ans = vector<string>();

    for (unsigned int hour = 0; hour < 12; ++hour) {
      for (unsigned int minute = 0; minute < 60; ++minute) {
        if (popcount(hour) + popcount(minute) == turnedOn) {
          ans.push_back(format("{}:{:02}", hour, minute));
        }
      }
    }

    return ans;
  }
};