JAVA // How do i make it case-insensitive?

Question

import java.util.Random;

public class MergeSortEx {

    public static void mergeSort(char[] array) {
        sortArray(array, 0, array.length);
    }

    private static void sortArray(char[] array, int start, int end) {
        if (end-start <2) 
            return;
    
            int mid = (start + end) / 2;
            sortArray(array, 0, mid);
            sortArray(array, mid, end);
            mergeArray(array, start, mid, end);
    }

    private static void mergeArray(char[] array, int start, int mid, int end) {
        char[] temp = new char[end - start];
        int t = 0, s = start, m = mid;

        while (s < mid && m < end) {
            if (array[s] < array[m])
                temp[t++] = array[s++];
            else
                temp[t++] = array[m++];
        }

        while (s < mid) {
            temp[t++] = array[s++];
        }
        while (m < end) {
            temp[t++] = array[m++];
        }
        
        for(int i=start;i<end;i++) {
            array[i]=temp[i-start];
        }
    }

    public static void main(String[] args) {
        char[] randomString = new char[20];
        Random rnd = new Random();

        for (int i = 0; i < 20; i++) {
            if (i < 10)
                randomString[i] = (char) (rnd.nextInt(6) + 'A');
            else
                randomString[i] = (char) (rnd.nextInt(6) + 'a');
        }

        System.out.println(randomString.length);
        for (int i = 0; i < 20; i++)
            System.out.print(randomString[i] + " ");
        
        mergeSort(randomString);
        System.out.println();
        for (int i = 0; i < 20; i++)
            System.out.print(randomString[i] + " ");
    }
}

I used the translator. It's a university algorithm assignment, Merge sort implemented successfully. Now, capital letters come out first, and lowercase letters come out. Can make the code case-insensitive? I want the results to be like this. ex) a AAB b C c c D d... plz help.

Answer 1

Instead of comparing using if (array[s] < array[m]) directly, convert the characters to uppercase before comparing, similar to what String.compareToIgnoreCase(...) does:

if (Character.toUpperCase(array[s]) < Character.toUpperCase(array[m]))

That is for sorting individual characters. For sorting String values, there are two ways to make a case-insensitive sort:

1. Use the predefined String.CASE_INSENSITIVE_ORDER Comparator .

    stringList.sort(String.CASE_INSENSITIVE_ORDER);

2. Use a Collator :

    Collator collator = Collator.getInstance(Locale.US); stringList.sort(collator);

   That will sort localized alphabets correctly, eg if you specified Locale.GERMANY , it would sort upper- and lower-case letters together, but will eg also sort Ð between D and E , and sort ß same as S .

Answer 2

Just replace:

while (s < mid && m < end) {
    if (arr[s] < arr[m])
        temp[t++] = arr[s++];
    else
        temp[t++] = arr[m++];
}

with

while (s < mid && m < end) {
    if (Character.toLowerCase(arr[s]) < Character.toLowerCase(arr[m]))
        temp[t++] = arr[s++];
    else
        temp[t++] = arr[m++];
}

Answer 3

If you want small letters come first like aAbbbBBBcCCCD then try following.
Instead of:

array[s] < array[m]

Use:

   private static boolean charCompare(char a, char b) {
        char ua = Character.toUpperCase(a);
        char ub = Character.toUpperCase(b); 
        if(ua == ub) {
            return a > b;
        } else {
            return ua < ub;
        }
    }

Output:

20
F E E A D A B C A E a e c f d f c a f e 
a a A A A B c c C d D e e E E E f f f F