CountingSort

package _Sort.Algorithm

/**
 * https://www.geeksforgeeks.org/counting-sort/
 * It is not a comparison based sorting.
 * It running time complexity is O(n) with space proportional to the range of data.
 * */
class CountingSort {

    fun sortArray(nums: IntArray) {
        val min = nums.min() ?: 0
        val max = nums.max() ?: 0
        var range = max - min + 1
        if (range <= 0) {
            range = 0
        }
        val countArray = IntArray(range)
        val output = IntArray(nums.size)
        //count each element in given array and place the count at the appropriate index
        for (num in nums) {
            countArray[num - min]++
        }
        //modify the count array by adding previous counts
        for (i in 1 until countArray.size) {
            countArray[i] += countArray[i - 1]
        }
        //set to output array and decreasing count array
        for (i in nums.size - 1 downTo 0) {
            val newIndex = countArray[nums[i] - min]
            output[newIndex - 1] = nums[i]
            //newIndex--
        }
        for (i in nums.indices) {
            nums[i] = output[i]
        }
        for (item in nums) {
            print(item)
            print(",")
        }
    }
}