Java merge and sort integer arrays without using pre-defined functions

George has a problem. He’s got two unordered integer arrays such as below:

{2, 3, 1}

{2, 5, 5, 8, 9, 13}

Now, he wants to merge these two and sort them in ascending order. He is not allowed to use any sort functions to solve this problem. The result should display:

[1, 2, 2, 3, 5, 5, 8, 9, 13]

His task is to define a function to merge and sort integer arrays without using pre-defined functions of Java. To solve this problem, let’s break down our solution into smaller steps.

First step is to merge:

static int[] mergeArray(int[] arr1, int[] arr2) {
    int[] mergedArr = new int[arr1.length + arr2.length];
    int index = arr2.length;
    for(int i = 0; i < arr2.length; i++) {
        mergedArr[i] = arr2[i];
    }
    for(int i = 0; i < arr1.length; i++) {
        mergedArr[i + index] = arr1[i];
    }
    return mergedArr;
}

Second step is to sort:

And then to sort it, we will implement Bubble sort algorithm. (Bubble sort, sometimes referred to as sinking sort, is a simple sorting algorithm that repeatedly steps through the list to be sorted, compares each pair of adjacent items and swaps them if they are in the wrong order. source: Wikipedia)

static int[] sortArray(int[] mergedArr) {
    for(int i = 0; i < mergedArr.length; i++) {
        for(int j = i + 1; j < mergedArr.length; j++) {
            int tmp = 0;
            if(mergedArr[i] > mergedArr[j]) {
                tmp = mergedArr[i];
                mergedArr[i] = mergedArr[j];
                mergedArr[j] = tmp;
            }
        }
    }
    return mergedArr;
}

This is to sort in ascending order. If you want to sort in descending order, just change the operand from > (greater than) to < (less than).

static int[] sortArray(int[] mergedArr) {
     for(int i = 0; i < mergedArr.length; i++) {
         for(int j = i + 1; j < mergedArr.length; j++) {
             int tmp = 0;
             if(mergedArr[i] < mergedArr[j]) {
                 tmp = mergedArr[i];
                 mergedArr[i] = mergedArr[j];
                 mergedArr[j] = tmp;
             }
         }
     }
     return mergedArr;
}

And that’s it! If you want the entire code, please refer to solution below:

import java.util.Arrays;
public class MyClass {
    public static void main(String args[]) {
        int[] arr1 = {2, 3, 1};
        int[] arr2 = {2, 5, 5, 8, 9, 13};
        System.out.print(Arrays.toString(sortArray(mergeArray(arr1, arr2))));
    }
    static int[] mergeArray(int[] arr1, int[] arr2) {
        int[] mergedArr = new int[arr1.length + arr2.length];
        int index = arr2.length;
        for(int i = 0; i < arr2.length; i++) {
            mergedArr[i] = arr2[i];
        }
        for(int i = 0; i < arr1.length; i++) {
            mergedArr[i + index] = arr1[i];
        }
        return mergedArr;
    }
    static int[] sortArray(int[] mergedArr) {
        for(int i = 0; i < mergedArr.length; i++) {
            for(int j = i + 1; j < mergedArr.length; j++) {
                int tmp = 0;
                if(mergedArr[i] > mergedArr[j]) {
                    tmp = mergedArr[i];
                    mergedArr[i] = mergedArr[j];
                    mergedArr[j] = tmp;
                }
            }
        }
        return mergedArr;
    }
}

Result:

[1, 2, 2, 3, 5, 5, 8, 9, 13]

I recommend using http://www.jdoodle.com to test it online if you don’t have any installed IDE on your local machines. If you have any questions, feel free to drop your comments 🙂