Binary Watch LeetCode solution in JavaScript

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/**
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 * @param {number} turnedOn
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 * @return {string[]}
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 */
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var readBinaryWatch = function (turnedOn) {
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  // _ _ _ _ 0-11 => 0000 - 1100
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  // _ _ _ _ _ _ 0-59 => 111011
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  let minutes = new Map();
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  let hours = new Map();
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  for (let i = 0; i < 12; i++) {
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    let ones = 0;
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    for (let j = 0; j < 5; j++) {
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      ones += (i >> j) & 1;
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    }
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    if (hours.has(ones)) {
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      prev = hours.get(ones);
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      prev.push(i);
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      hours.set(ones, prev);
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    } else {
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      hours.set(ones, [i]);
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    }
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    //0001 1
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    //0010 2
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    //0011 3
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    //0100 4
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    //0101 5
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    //0110 6
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    //0111 7
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    //1000 8
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    //1001 9
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    //1010 10
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    //1011 11
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  }
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  for (let i = 0; i < 60; i++) {
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    let ones = 0;
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    for (let j = 0; j < 7; j++) {
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      ones += (i >> j) & 1;
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    }
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    if (minutes.has(ones)) {
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      let prev = minutes.get(ones);
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      prev.push(i);
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      minutes.set(ones, prev);
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    } else {
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      minutes.set(ones, [i]);
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    }
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  }
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  let result = [];
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  for (let i = 0; i <= turnedOn; i++) {
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    if (hours.has(i)) {
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      let h = hours.get(i);
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      for (let j = 0; j < h.length; j++) {
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        let ones = turnedOn - i;
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        if (minutes.has(ones)) {
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          let min = minutes.get(ones);
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          for (let k = 0; k < min.length; k++) {
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            let minlen = (min[k] + "").length;
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            if (minlen == 1) {
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              minlen = "0" + min[k];
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            } else {
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              minlen = min[k];
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            }
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            result.push(h[j] + ":" + minlen);
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          }
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        }
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      }
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    }
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  }
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  return result;
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};