sort.js

/**
 * Efficient sort implementations.
 *
 * Note: These sort implementations were created to compare different sorting algorithms in JavaScript.
 * Don't use them if you don't know what you are doing. Native Array.sort is almost always a better choice.
 *
 * @module sort
 */

import * as math from './math.js'

/**
 * @template T
 * @param {Array<T>} arr
 * @param {number} lo
 * @param {number} hi
 * @param {function(T,T):number} compare
 */
export const _insertionSort = (arr, lo, hi, compare) => {
  for (let i = lo + 1; i <= hi; i++) {
    for (let j = i; j > 0 && compare(arr[j - 1], arr[j]) > 0; j--) {
      const tmp = arr[j]
      arr[j] = arr[j - 1]
      arr[j - 1] = tmp
    }
  }
}

/**
 * @template T
 * @param {Array<T>} arr
 * @param {function(T,T):number} compare
 * @return {void}
 */
export const insertionSort = (arr, compare) => {
  _insertionSort(arr, 0, arr.length - 1, compare)
}

/**
 * @template T
 * @param {Array<T>} arr
 * @param {number} lo
 * @param {number} hi
 * @param {function(T,T):number} compare
 */
const _quickSort = (arr, lo, hi, compare) => {
  if (hi - lo < 42) {
    _insertionSort(arr, lo, hi, compare)
  } else {
    const pivot = arr[math.floor((lo + hi) / 2)]
    let i = lo
    let j = hi
    while (true) {
      while (compare(pivot, arr[i]) > 0) {
        i++
      }
      while (compare(arr[j], pivot) > 0) {
        j--
      }
      if (i >= j) {
        break
      }
      // swap arr[i] with arr[j]
      // and increment i and j
      const arri = arr[i]
      arr[i++] = arr[j]
      arr[j--] = arri
    }
    _quickSort(arr, lo, j, compare)
    _quickSort(arr, j + 1, hi, compare)
  }
}

/**
 * This algorithm beats Array.prototype.sort in Chrome only with arrays with 10 million entries.
 * In most cases [].sort will do just fine. Make sure to performance test your use-case before you
 * integrate this algorithm.
 *
 * Note that Chrome's sort is now a stable algorithm (Timsort). Quicksort is not stable.
 *
 * @template T
 * @param {Array<T>} arr
 * @param {function(T,T):number} compare
 * @return {void}
 */
export const quicksort = (arr, compare) => {
  _quickSort(arr, 0, arr.length - 1, compare)
}