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/*

* Places the `k` smallest elements in `array` in the first `k` indices: `[0..k-1]`

* Modifies the passed in array *in place*

* Returns a slice of the wanted elements for convenience

* Efficient mainly because it never performs a full sort.

*

* The only guarantees are that:

*

* - The `k`th element is in its final sort index (if the array were to be sorted)

* - All elements before index `k` are smaller than the `k`th element

*

* [Reference](http://en.wikipedia.org/wiki/Quickselect)

*/

export function quickSelectSearch (array, k) {

if (!array || array.length <= k) {

throw new Error('Invalid arguments')

}

let from = 0

let to = array.length - 1

while (from < to) {

let left = from

let right = to

const pivot = array[Math.ceil((left + right) * 0.5)]

while (left < right) {

if (array[left] >= pivot) {

const tmp = array[left]

array[left] = array[right]

array[right] = tmp

--right

} else {

++left

}

}

if (array[left] > pivot) {

--left

}

if (k <= left) {

to = left

} else {

from = left + 1

}

}

return array

}

/* ---------------------------------- Test ---------------------------------- */

// const arr = [1121111, 21, 333, 41, 5, 66, 7777, 28, 19, 11110]

// quickSelectSearch(arr, 5) // [ 19, 21, 28, 41, 5, 66, 333, 11110, 1121111, 7777 ]

// quickSelectSearch(arr, 2) // [ 19, 5, 21, 41, 28, 333, 11110, 1121111, 7777, 66 ]

// quickSelectSearch(arr, 7) // [ 19, 5, 21, 41, 28, 66, 333, 7777, 11110, 1121111 ]