Candy LeetCode solution in JavaScript

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/**
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 * @param {number[]} ratings
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 * @return {number}
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 */
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var candy = function (ratings) {
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  const n = ratings.length;
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  let candies = [...Array(n)].fill(1);
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  let index = 0;
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  let copy = [ratings[0]];
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  let isDecreasing = true;
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  for (let i = 1; i < n; i++) {
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    if (ratings[i] > ratings[i - 1]) {
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      isDecreasing = false;
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      break;
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    }
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    /* In case of decreasing sequence, make a copy of the current rating, but in inverted format */
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    copy.unshift(ratings[i]);
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  }
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  if (isDecreasing) {
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    ratings = copy;
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  } else {
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    copy = [];
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  }
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  while (index >= 0) {
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    if (index >= n) {
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      break;
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    }
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    if (
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      ratings[index] > ratings[index + 1] &&
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      candies[index + 1] >= candies[index]
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    ) {
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      candies[index] = candies[index] + 1;
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      index = Math.max(-1, index - 2);
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    } else if (
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      ratings[index] > ratings[index - 1] &&
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      candies[index - 1] >= candies[index]
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    ) {
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      candies[index] = candies[index - 1] + 1;
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    }
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    index++;
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  }
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  return candies.reduce((sum, candy) => sum + candy, 0);
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};