Minimum Adjacent Swaps to Reach the Kth Smallest Number LeetCode solution in JavaScript

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var getMinSwaps = function (num, k) {
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  const digits = [...num];
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  const len = digits.length;
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  // helper function to swap elements in digits in place
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  const swap = (i, j) => ([digits[i], digits[j]] = [digits[j], digits[i]]);
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  // helper function to reverse elements in digits from i to the end of digits
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  const reverse = (i) => {
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    for (let j = len - 1; i < j; ++i && --j) {
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      swap(i, j);
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    }
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  };
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  // helper to get the next smallest permutation for digits
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  const nextPermutation = () => {
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    // from right to left, find the first decreasing index
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    // in digits and store it as i
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    let i = len - 2;
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    while (digits[i] >= digits[i + 1]) {
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      i--;
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    }
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    // from right to left, find the first index in digits
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    // that is greater than element at i
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    let j = len - 1;
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    while (digits[j] <= digits[i]) {
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      j--;
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    }
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    // swap the 2 elements at i and j
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    swap(i, j);
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    // reverse all elements after i because we know that
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    // all elements after i are in ascending order
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    // from right to left
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    reverse(i + 1);
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  };
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  // find the next permutation k times
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  for (let i = 0; i < k; i++) {
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    nextPermutation();
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  }
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  // find out how many swaps it will take to get to the
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  // kth permutation by finding out how many swaps
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  // it takes to put digits back to its original state
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  let numSwaps = 0;
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  for (let i = 0; i < len; i++) {
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    let j = i;
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    // find the first element in digits to matches
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    // num[i] and hold its place at j
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    while (num[i] !== digits[j]) {
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      j++;
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    }
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    // move the element at j to i while counting the
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    // number of swaps
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    while (i < j) {
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      swap(j, j - 1);
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      numSwaps++;
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      j--;
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    }
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  }
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  return numSwaps;
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};