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Quicksort in JavaScript
/**
* An implementation for Quicksort. Doesn't
* perform as well as the native Array.sort
* and also runs the risk of a stack overflow
*
* Tests with:
*
* var array = [];
* for(var i = 0; i < 20; i++) {
* array.push(Math.round(Math.random() * 100));
* }
*
* Quicksort.sort(array);
*
* @author Paul Lewis
*/
var Quicksort = (function() {
/**
* Swaps two values in the heap
*
* @param {int} indexA Index of the first item to be swapped
* @param {int} indexB Index of the second item to be swapped
*/
function swap(array, indexA, indexB) {
var temp = array[indexA];
array[indexA] = array[indexB];
array[indexB] = temp;
}
/**
* Partitions the (sub)array into values less than and greater
* than the pivot value
*
* @param {Array} array The target array
* @param {int} pivot The index of the pivot
* @param {int} left The index of the leftmost element
* @param {int} left The index of the rightmost element
*/
function partition(array, pivot, left, right) {
var storeIndex = left,
pivotValue = array[pivot];
// put the pivot on the right
swap(array, pivot, right);
// go through the rest
for(var v = left; v < right; v++) {
// if the value is less than the pivot's
// value put it to the left of the pivot
// point and move the pivot point along one
if(array[v] < pivotValue) {
swap(array, v, storeIndex);
storeIndex++;
}
}
// finally put the pivot in the correct place
swap(array, right, storeIndex);
return storeIndex;
}
/**
* Sorts the (sub-)array
*
* @param {Array} array The target array
* @param {int} left The index of the leftmost element, defaults 0
* @param {int} left The index of the rightmost element,
defaults array.length-1
*/
function sort(array, left, right) {
var pivot = null;
if(typeof left !== 'number') {
left = 0;
}
if(typeof right !== 'number') {
right = array.length - 1;
}
// effectively set our base
// case here. When left == right
// we'll stop
if(left < right) {
// pick a pivot between left and right
// and update it once we've partitioned
// the array to values < than or > than
// the pivot value
pivot = left + Math.ceil((right - left) * 0.5);
newPivot = partition(array, pivot, left, right);
// recursively sort to the left and right
sort(array, left, newPivot - 1);
sort(array, newPivot + 1, right);
}
}
return {
sort: sort
};
})();
@minsooshin

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@minsooshin minsooshin commented Feb 27, 2014

At the end of sort method, doesn't it need to add return array?

@dijs

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@dijs dijs commented Apr 10, 2014

It's an in-place sort.

@hammeiam

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@hammeiam hammeiam commented Apr 23, 2016

Line 38 should be 'right'

@denis-adobe

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@denis-adobe denis-adobe commented Dec 9, 2016

Line 71 should be 'right' either

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