Is there a best way to approach this ?

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Hello guys, i'm looking to refactor this method. It split an Array of integers int[] in two smaller ones (array1 and array2) and return those as an Object[]{array1,array2} I'm pretty sure i can give some fresh to this algorithm. Someone would like to review this code ?

private static Object[] inTwoSmallOnes(int[] numbers) {
        int smallOnesLength = (numbers.length / 2);
        int[] array1 = new int[smallOnesLength];
        int[] array2 = new int[smallOnesLength];
        for (int i = 0; i < numbers.length; i++) {
            if (i < (numbers.length / 2)) {
                array1[i] = numbers[i];
            } else {
                array2[i - (numbers.length / 2)] = numbers[i];
            }
        }
        return new Object[]{array1,array2};
    }

Happy coding !

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Guadalupe Gagnon

Level 37 , Tampa, United States

10 May 2019, 19:17

Using the Arrays class you could easily split into 2 and CPU wise it runs FAST. Other than that in your code you could make it more efficient by using 2 while loops and 1 counter. While loops run faster than for loops. Run this code to see the differences:

Guadalupe Gagnon

Level 37 , Tampa, United States

10 May 2019, 19:18

useful

public class Solution {
    public static void main(String[] args) throws Exception {
        int length = 1000000; // enter length here, even numbers only
        int[] numbers = new int[length];
        for(int i = 0; i < length; i++) numbers[i] = i;
        inTwoUsingWhile(numbers);
        inTwoUsingFor(numbers);
        inTowUsingArrays(numbers);
    }

    /*Put the methods inside this method (in main) to test that the split is occuring
      properly. I would set the length low, something like 6*/
    private static void printData(int[][] inTwoUsingWhile) {
        System.out.print("\tFirst half : " + Arrays.toString(inTwoUsingWhile[0]));
        System.out.println("\tSecond half: " + Arrays.toString(inTwoUsingWhile[1]));
    }


    private static int[][] inTwoUsingWhile(int[] numbers) {
        long start = System.currentTimeMillis();
        int smallOnesLength = numbers.length / 2;
        int[] array1 = new int[smallOnesLength], array2 = new int[smallOnesLength];
        int i = 0;
        while (i < smallOnesLength) {
            array1[i] = numbers[i];
            i++;

        }
        while(i < numbers.length){
            array2[i-smallOnesLength] = numbers[i];
            i++;
        }
        long end = System.currentTimeMillis();
        System.out.println("Using 2 'while' loops split the array in " + (end-start) +"ms");
        return new int[][]{array1,array2};
    }

Guadalupe Gagnon

Level 37 , Tampa, United States

10 May 2019, 19:19

solution

private static int[][] inTwoUsingFor(int[] numbers) {
        long start = System.currentTimeMillis();
        int smallOnesLength = (numbers.length / 2);
        int[] array1 = new int[smallOnesLength];
        int[] array2 = new int[smallOnesLength];
        for (int i = 0; i < numbers.length; i++) {
            if (i < (numbers.length / 2)) {
                array1[i] = numbers[i];
            } else {
                array2[i - (numbers.length / 2)] = numbers[i];
            }
        }
        long end = System.currentTimeMillis();
        System.out.println("Using a 'for' loops split the array in " + (end-start) +"ms");
        return new int[][]{array1,array2};
    }

    private static int[][] inTowUsingArrays(int[] numbers){
        long start = System.currentTimeMillis();
        int half = numbers.length/2;
        int[] first = Arrays.copyOfRange(numbers,0,half);
        int[] second = Arrays.copyOfRange(numbers,half,numbers.length);
        long end = System.currentTimeMillis();
        System.out.println("Using Arrays class split the array in " + (end-start) +"ms");
        return new int[][] {first, second};
    }
}

Guadalupe Gagnon

Level 37 , Tampa, United States

10 May 2019, 19:21

useful

Splitting an array of 100,000 numbers takes (on my computer): 8 ms using while loops 17 ms using a for loop with an if-else (double the time) 2 ms using the Arrays class (clearly the winner)

Julien

Level 15 , Paris, France

10 May 2019, 20:19

Thank you for your answer. I did myself the test and had the same result. I don't have already the reflex to see at the doc some usefull methods,I didn't know about the Arrays class, i tried to reinvent the wheel :D

Guadalupe Gagnon

Level 37 , Tampa, United States

10 May 2019, 20:31

useful

You are learning. I did the same thing you did when I first started too, we all do. Practicing with things like you are doing now is the best way to learn. By the way: if you increase the length to 100000000 instead of 1000000, the times change: 262ms using the while loops (quite a bit slower than the other 2) 182ms using the for loop 180ms using the arrays class (still the fastest but not by much)

Julien

Level 15 , Paris, France

10 May 2019, 18:50

Of course, we assume that the user call this with an Array with even number of elements :-)