package main

/*
 * Heap sort - https://en.wikipedia.org/wiki/Heapsort
 */

func sift(arr []int, i int, arrLen int) []int {
    done := false

    tmp       := 0
    maxChild  := 0
    
    for (i * 2 + 1 < arrLen) && (!done) {
        if i * 2 + 1 == arrLen - 1 {
            maxChild = i * 2 + 1
        } else if (arr[i * 2 + 1] > arr[i * 2 + 2]) {
            maxChild = i * 2 + 1
        } else {
            maxChild = i * 2 + 2
        }
    
        if arr[i] < arr[maxChild] {
            tmp = arr[i]
            arr[i] = arr[maxChild]
            arr[maxChild] = tmp
            i = maxChild
        } else {
            done = true
        }
    }

    return arr
}

func HeapSort(arr []int) {
    i := 0
    tmp := 0

    for i = len(arr) / 2 - 1; i >= 0; i-- {
        arr = sift(arr, i, len(arr))
    }

    for i = len(arr) - 1; i >= 1; i-- {
        tmp = arr[0];
        arr[0] = arr[i];
        arr[i] = tmp;
        arr = sift(arr, 0, i);
    }
}