In-place Partition func in quicksort

ˋˋˋ

function partition(nums, left, right) {

  const pivot = const pivotPos = nums[right]

  // left bucket is the contiguous part where numbers are smaller than pivot

  // right bucket is the contiguous part where numbers are greater than pivot

  let leftBucketExclusiveEnd = left

  for (let curPos = leftBucketExclusiveEnd; curPos < right - 1; curPos++) {

  if (nums[curPos] < pivot) {

    swap(nums, curPos, leftBucketExclusiveEnd)

    leftBucketExclusiveEnd++;

  }

}

// place the pivot between two segments

swap (nums, leftBucketExclusiveEnd, pivotPos)

return pivotPos

}

ˋˋˋ

The left bucket range is nums[0 ... leftBucketExclusiveEnd - 1], we start with an empty bucket, and we try to check the exclusive end number. If that number is smaller than pivot, we push this number into bucket ( by moving the swapping the leftBucketExclusiveEnd value with that number, and move leftBucketExclusiveEnd point to next element)

This trick make use of the charateristic that this is a contiguous list. So that we can define two ranges by ony one pointer (leftBucketExclusiveEnd)