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MergeSort.kt
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MergeSort.kt
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/*
* Copyright (c) 2017 Kotlin Algorithm Club
*
* Permission is hereby granted, free of charge, to any person obtaining a copy
* of this software and associated documentation files (the "Software"), to deal
* in the Software without restriction, including without limitation the rights
* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
* copies of the Software, and to permit persons to whom the Software is
* furnished to do so, subject to the following conditions:
*
* The above copyright notice and this permission notice shall be included in all
* copies or substantial portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
* SOFTWARE.
*/
package io.uuddlrlrba.ktalgs.sorts
/**
* Invented in 1945 by John von Neumann, merge sort is an efficient algorithm using the divide and conquer approach
* which is to divide a big problem into smaller problems and solve them. Conceptually, a merge sort works as follows:
* 1) Divide the unsorted list into n sublists, each containing 1 element (a list of 1 element is considered sorted).
* 2) Repeatedly merge sublists to produce new sorted sublists until there is only 1 sublist remaining.
*/
@ComparisonSort
@StableSort
class MergeSort: AbstractSortStrategy() {
override fun <T : Comparable<T>> perform(arr: Array<T>) {
val aux = arr.clone()
sort(arr, aux, 0, arr.size - 1)
}
private fun <T : Comparable<T>> sort(arr: Array<T>, aux: Array<T>, lo: Int, hi: Int) {
if (hi <= lo) return
val mid = (lo + hi) / 2
sort(arr, aux, lo, mid)
sort(arr, aux, mid + 1, hi)
merge(arr, aux, lo, mid, hi)
}
private fun <T : Comparable<T>> merge(arr: Array<T>, aux: Array<T>, lo: Int, mid: Int, hi: Int) {
System.arraycopy(arr, lo, aux, lo, hi - lo + 1)
var i = lo
var j = mid + 1
for (k in lo..hi) {
when {
i > mid -> arr[k] = aux[j++]
j > hi -> arr[k] = aux[i++]
aux[j] < aux[i] -> arr[k] = aux[j++]
else -> arr[k] = aux[i++]
}
}
}
}