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/**
* [QuickSelect](https://www.geeksforgeeks.org/quickselect-algorithm/) is an algorithm to find the kth smallest number
*
* Notes:
* -QuickSelect is related to QuickSort, thus has optimal best and average
* -case (O(n)) but unlikely poor worst case (O(n^2))
* -This implementation uses randomly selected pivots for better performance
*
* @complexity: O(n) (on average )
* @complexity: O(n^2) (worst case)
* @flow
*/
function QuickSelect(items, kth) {
if (kth < 1 || kth > items.length) {
throw new RangeError('Index Out of Bound')
}
return RandomizedSelect(items, 0, items.length - 1, kth)
}
function RandomizedSelect(items, left, right, i) {
if (left === right) return items[left]
const pivotIndex = RandomizedPartition(items, left, right)
const k = pivotIndex - left + 1
if (i === k) return items[pivotIndex]
if (i < k) return RandomizedSelect(items, left, pivotIndex - 1, i)
return RandomizedSelect(items, pivotIndex + 1, right, i - k)
}
function RandomizedPartition(items, left, right) {
const rand = getRandomInt(left, right)
Swap(items, rand, right)
return Partition(items, left, right)
}
function Partition(items, left, right) {
const x = items[right]
let pivotIndex = left - 1
for (let j = left; j < right; j++) {
if (items[j]