Algorithms | Quick Sort | JavaScript

quick-sort.js

// Quick Sort Algorithm implemented in JavaScript
// By @hackerrdave

function quickSort(arr) {
  if (arr.length < 2) {
    return arr;
  }
  
  let pivot = arr[0]; //let pivot point be the first element
  let lesser = []; //track elements < the pivot value
  let greater = []; //track elements greater >= the pivot value
  
  for (let i = 1; i < arr.length; i++) {
    if (arr[i] < pivot) {
      lesser.push(arr[i]);
    } else {
      greater.push(arr[i]);
    }
  }
  
  //recurse into lesser and greater collections, setting up
  //new pivots and lesser/greater collections. After bubbling
  //back up concat the lesser singular-array value with the pivot
  //and greater singular-value array
  return quickSort(lesser).concat(pivot, quickSort(greater));
}

//usage:
quickSort([4,2,8,3,6,9,1]); //=> [1,2,3,4,6,8,9]