JS functions: linear time counting sort for integers

counting-sort.js

function countingSort(arr, min, max) {
	var i, z = 0, count = [];
	for (i = min; i <= max; i++) {
		count[i] = 0;
	}
	for (i=0; i < arr.length; i++) {
		count[arr[i]]++;
	}
	for (i = min; i <= max; i++) {
		while (count[i]-- > 0) {
			arr[z++] = i;
		}
	}
	return arr;
}

function countingSortUnknownRange(arr) {
	var counts = [];
	for (var i=0; i < arr.length; i++) {
		if (counts[arr[i]] === undefined) {
			counts[arr[i]] = 1;
		} else {
			counts[arr[i]]++;
		}
	}

	var z = 0;
	counts.forEach(function(count, val) {
		while (count-- > 0) {
			arr[z++] = val;
		}
	});

	return arr;
}

// 1. Map each item in the input array to an integer
//    representing its proper order in the resulting array.
// 2. Use each integer as an index in a sparse array to point
//    to an array of the values which returned that integer.
// 3. Replace the items in the passed array, but with the new order
//    they have in the sparse array (or in reverse if desc is truthy).
function mapCountingSort(arr, mapFn, desc) {
	var z = desc ? arr.length : 0;
	var valsByInt = [];

	for (var i=0; i < arr.length; i++) {
		var int = mapFn(arr[i]); // 1
		if (valsByInt[int] === undefined) {
			valsByInt[int] = [arr[i]]; // 2
		} else {
			valsByInt[int].push(arr[i]);
		}
	}

	valsByInt.forEach(desc ? function(vals, val) {
		for (var i = 0; i < vals.length; i++) {
			arr[--z] = vals[i]; // 3
		}
	} : function(vals, val) {
		for (var i = 0; i < vals.length; i++) {
			arr[z++] = vals[i]; // 3
		}
	});
	return arr;
}