f, Java - rextester

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/**
 *  Iterative Merge sort implementation
 *
 *  @author: Jayesh Chandrapal
 */

import java.util.*;
import java.lang.*;

class Rextester
{  
    public static void main(String args[])
    {
        int[] nums = {7,8,9,4,6,5,2,4,3,1,6,8,7,9,2,4,3,5,6};
        
        printArray(nums);
        
        mergeSort(nums);
        
        printArray(nums);
    }
    
    public static void printArray(int[] nums) {
        for(Integer num : nums)
            System.out.print(num + " ");
        System.out.println();
    }
    
    public static void mergeSort(int[] nums) {
        if(nums == null) {
            return;
        }
        
        if(nums.length > 1) {
            int mid = nums.length / 2;
            
            // Split left part
            int[] left = new int[mid];
            for(int i = 0; i < mid; i++) {
                left[i] = nums[i];
            }
            
            // Split right part
            int[] right = new int[nums.length - mid];
            for(int i = mid; i < nums.length; i++) {
                right[i - mid] = nums[i];
            }
            
            mergeSort(left);
            mergeSort(right);
            
            int i = 0;
            int j = 0;
            int k = 0;
            
            // Merge left and right arrays
            while(i < left.length && j < right.length) {
                if(left[i] < right[j]) {
                    nums[k] = left[i];
                    i++;
                } else {
                    nums[k] = right[j];
                    j++;
                }
                k++;
            }
            
            // Collect remaining elements
            while(i < left.length) {
                nums[k] = left[i];
                i++; k++;
            }
            
            while(j < right.length) {
                nums[k] = right[j];
                j++; k++;
            }
        }
    }
}

[ + ] Show input
Compilation time: 0.52 sec, absolute running time: 0.13 sec, cpu time: 0.06 sec, memory peak: 19 Mb, absolute service time: 0,67 sec