Btukfyl

starting Java coder here. I was wondering how to change my code so it would sort array by always swapping the biggest value to first. Sample output should be:

[3, 1, 2, 0] [3, 2, 1, 0].

public class Sorting {



static void biggest(int arr, int start, int end) {

    for (start = 0; start < arr.length; start++) {

        for (end = start + 1; end < arr.length; end++) {

            if (arr[start] < arr[end]) {

                int temp = arr[end];

                arr[end] = arr[start];

                arr[start] = temp;

                System.out.println(Arrays.toString(arr));



            }

        }

    }

}



public static void main(String args) {

    int arr = {0, 1, 2, 3};

    int temp = 0;

    for (int i = 0; i < 4; ++i) {

        biggest(arr, temp, 4 - 1);

        for (int j = 0; j < 4; ++j) {

        }

        ++temp;

    }

}

Thanks in advance,
- Em

If you just want the sort to be successful, I suggest taking advantage of Java's built in sort method then reversing the list as suggested here:

Arrays.sort(arr);

ArrayUtils.reverse(arr); 

But it sounds like the spirit of your question is to modify your code for this purpose. Here's the solution I came up with:

import java.util.Arrays;



public class Sorting {



static void biggest(int arr) {

    for (int i = 0; i < arr.length; i++) {

        System.out.println(Arrays.toString(arr));

        int max, maxAt = i;

        for (int j = i; j < arr.length; j++) {

            maxAt = arr[j] > arr[maxAt] ? j : maxAt;

        }

        max = arr[maxAt];

        if (arr[i] < max) {

            arr[maxAt] = arr[i];

            arr[i] = max;

        }

    }

}



public static void main(String args) {

    int arr = {0, 1, 2, 3};

    biggest(arr);

    System.out.println(Arrays.toString(arr));

}

}

First off, you had a lot of extra code that you didn't need. It's a bad idea to have a loop in your main. That should be handled by the helper function. You also had a lot of redundant declarations (like start and end). You were on the right track with your helper function, but because of your main loop your time complexity was 0(n²). Eliminating that allows mine to be O(logn). Complexity aside, the key difference in terms of logic is here in your internal loop:

for (end = start + 1; end < arr.length; end++) {

        if (arr[start] < arr[end]) {

            int temp = arr[end];

            arr[end] = arr[start];

            arr[start] = temp;

In this loop you're switching the array entry with the first one you find that's bigger. This will result in unwanted early switches (like 1 & 2). Here is my solution:

for (int j = i; j < arr.length; j++) {

        maxAt = arr[j] > arr[maxAt] ? j : maxAt;

    }

    max = arr[maxAt];

    if (arr[i] < max) {

        arr[maxAt] = arr[i];

        arr[i] = max;

    }

The key difference is that I search for the maximum value entry following the one we're swapping. That way as we proceed through the array we will always bring forward the next biggest.

Best of luck learning Java I hope this helps!