Count Number of Nice Subarrays LeetCode solution in JavaScript

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/**
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 * @param {number[]} nums
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 * @param {number} k
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 * @return {number}
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 */
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var numberOfSubarrays = function (nums, k) {
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  const len = nums.length;
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  const pre = new Array(len).fill(-1);
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  const post = new Array(len).fill(len);
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  let lastOcc = -1;
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  for (let i = 0; i < len; i++) {
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    pre[i] = lastOcc;
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    if (nums[i] & 1) lastOcc = i;
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  }
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  lastOcc = len;
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  for (let i = len - 1; i >= 0; i--) {
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    post[i] = lastOcc;
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    if (nums[i] & 1) lastOcc = i;
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  }
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  let l = 0,
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    r = 0,
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    oddCount = 0;
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  let ans = 0;
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  for (; r < len; r++) {
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    while (l < len && !(nums[l] & 1)) l++;
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    if (nums[r] & 1) oddCount++;
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    if (oddCount == k) {
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      let leftCount = l - pre[l];
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      let rightCount = post[r] - r;
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      ans += leftCount * rightCount;
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      oddCount--;
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      l++;
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    }
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  }
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  return ans;
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};