2020-10-31 17:33:26 +02:00
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/*
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* Places the `k` smallest elements in `array` in the first `k` indices: `[0..k-1]`
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* Modifies the passed in array *in place*
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* Returns a slice of the wanted elements for convenience
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* Efficient mainly because it never performs a full sort.
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*
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* The only guarantees are that:
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*
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* - The `k`th element is in its final sort index (if the array were to be sorted)
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* - All elements before index `k` are smaller than the `k`th element
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*
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* [Reference](http://en.wikipedia.org/wiki/Quickselect)
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*/
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2023-10-03 23:08:19 +02:00
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export function quickSelectSearch(array, k) {
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2020-10-31 17:33:26 +02:00
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if (!array || array.length <= k) {
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2020-10-31 17:53:08 +02:00
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throw new Error('Invalid arguments')
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2020-10-31 17:33:26 +02:00
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}
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2020-10-31 17:53:08 +02:00
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let from = 0
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let to = array.length - 1
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2020-10-31 17:33:26 +02:00
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while (from < to) {
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2020-10-31 17:53:08 +02:00
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let left = from
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let right = to
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const pivot = array[Math.ceil((left + right) * 0.5)]
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2020-10-31 17:33:26 +02:00
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while (left < right) {
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if (array[left] >= pivot) {
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2020-10-31 17:53:08 +02:00
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const tmp = array[left]
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array[left] = array[right]
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array[right] = tmp
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--right
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2020-10-31 17:33:26 +02:00
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} else {
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2020-10-31 17:53:08 +02:00
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++left
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2020-10-31 17:33:26 +02:00
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}
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}
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if (array[left] > pivot) {
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2020-10-31 17:53:08 +02:00
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--left
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2020-10-31 17:33:26 +02:00
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}
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if (k <= left) {
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2020-10-31 17:53:08 +02:00
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to = left
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2020-10-31 17:33:26 +02:00
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} else {
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2020-10-31 17:53:08 +02:00
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from = left + 1
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2020-10-31 17:33:26 +02:00
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}
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}
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2020-10-31 17:53:08 +02:00
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return array
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2020-10-31 17:33:26 +02:00
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}
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/* ---------------------------------- Test ---------------------------------- */
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2021-10-11 12:29:03 +02:00
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// const arr = [1121111, 21, 333, 41, 5, 66, 7777, 28, 19, 11110]
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// quickSelectSearch(arr, 5) // [ 19, 21, 28, 41, 5, 66, 333, 11110, 1121111, 7777 ]
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// quickSelectSearch(arr, 2) // [ 19, 5, 21, 41, 28, 333, 11110, 1121111, 7777, 66 ]
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// quickSelectSearch(arr, 7) // [ 19, 5, 21, 41, 28, 66, 333, 7777, 11110, 1121111 ]
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