如何在Node.js上编写快速排序

Question

I'm continue trying to write a alrorithms on Node.js like on the book Algorithms, 4th ed. Sedgewick, Wayne. There all the examples written on Java.

I have this quick sort module:

"use strict";

const _ = require('lodash');

module.exports = (function () {

  function _partition(array, lo, hi) {
    let i = lo;
    let j = hi + 1;
    let v = array[lo];

    while (true) {
      while (_less(array[++i], v)) {
        if (i === hi) {
          break;
        }
      }
      while (_less(v, array[--j])) {
        if (j === lo) {
          break;
        }
      }
      if (i >= j) {
        break;
      }
      _exch(array, i, j);
    }
    _exch(array, lo, j);
    return j;
  }

  function sort(array) {
    _sort(array, 0, array.length - 1);
  }

  function _sort(array, lo, hi) {
    if (hi <= lo) {
      return null;
    }

    let j = _partition(array, lo, hi);

    _sort(array, lo, j - 1);
    _sort(array, j + 1, hi);
  }

  function _less(array, i, min) {
    return array[i] < array[min];
  }

  function _exch(array, i, min) {
    let temp = array[i];
    array[i] = array[min];
    array[min] = temp;
  }

  return {
    sort: sort
  };

})();

I use mocha and chai for testing with this function:

function isSorted(array) {
  for(let i = 1, size = array.length; i < size; i++) {
    if (array[i] < array[i-1]) {
      return false;
    }
  }
  return true;
}

and quick sort not working. I need the same implementation as in book, but on js.

You can see original implementation here: quick sort in java

Answer 1

That implementation is ugly.

Sorry, I won't be able to help you answer a course question, but here is the beauty of a functionally recursive version of quicksort. Never, ever, use the above in javascript.

In ES6

A functionally recursive quicksort.

const quicksort = ([head, ...tail]) => head === undefined ? [] : 
  [...quicksort([...tail.filter(a => a <= head)]), head, ...quicksort([...tail.filter(a => a > head)])];

Usage

console.log(quicksort([1,3,1,0,6,8,9,12,15,22,54, 111,12,2,3,4,5,6,7,-1]));

Answer 2

Your function _less uses indexes as arguments:

  function _less(array, i, min) {
    return array[i] < array[min];

but you call it with array elements values :

 let v = array[lo];
 while (_less(array[++i], v)

(and omit first argument array - is it legal in JS?)