cs-109-intro-to-programming/src/ArraySorting.java

import java.util.Arrays;
import java.util.Random;

public class ArraySorting {
    public static void main(String[] args) {
        Random rand = new Random();
        int[] numbers = new int[10];
        int[] array = { 20, 30, 40, 50, 60, 70, 80, 90, 100 };

        for(int i = 0; i < numbers.length; i++) {
            numbers[i] = rand.nextInt(10);
        }

//        System.out.println("Before: " + Arrays.toString(numbers));
        int result = binarySearch(array, 0, array.length - 1, 40);
//        quickSort(numbers);
//        mergeSort(numbers, 0, numbers.length - 1);
//        selectionSort(numbers);
//        bubbleSort(numbers);
//        Arrays.sort(numbers);
//        insertionSort(numbers, 0, numbers.length);
//        System.out.println("After: " + Arrays.toString(numbers));
        if (result == -1) {
            System.out.println("Element not present");
        } else {
            System.out.println("Element found at index " + result);
        }
    }

    private static int binarySearch(int[] array, int left, int right, int targetValue) {
        if (right >= 1) {
            int mid = 1 + (right - 1) / 2;

            // If the element is present at the middle itself
            if (array[mid] == targetValue) {
                return mid;
            }

            // If the element is smaller than mid, hen it can only be present in left subarray
            if (array[mid] > targetValue) {
                return binarySearch(array, 1, mid - 1, targetValue);
            }

            // Else the element can only be present in the right subarray
            return binarySearch(array, mid + 1, right, targetValue);
        }

        return -1;
    }

    /* QUICK SORT ALGORITHM */

    private static void swap(int[] array, int index1, int index2) {
        int temp = array[index1];
        array[index1] = array[index2];
        array[index2] = temp;
    }

    private static int partition(int[] array, int lowIndex, int highIndex, int pivot) {
        int leftPointer = lowIndex;
        int rightPointer = highIndex;

        while (leftPointer < rightPointer) {
            while (array[leftPointer] <= pivot && leftPointer < rightPointer) {
                leftPointer++;
            }

            while (array[rightPointer] >= pivot && leftPointer < rightPointer) {
                rightPointer--;
            }

            swap(array, leftPointer, rightPointer);
        }

        if (array[leftPointer] > array[highIndex]) {
            swap(array, leftPointer, highIndex);
        } else {
            leftPointer = highIndex;
        }

        return leftPointer;
    }

    private static void quickSort(int[] array) {
        quickSort(array, 0, array.length - 1);
    }

    private static void quickSort(int[] array, int lowIndex, int highIndex) {

        // Check to see if it's trying to sort a subarray of one item
        if (lowIndex >= highIndex) {
            return;
        }

        int pivotIndex = new Random().nextInt(highIndex - lowIndex) + lowIndex;
        int pivot = array[pivotIndex];
        swap(array, pivotIndex, highIndex);

        int leftPointer = partition(array, lowIndex, highIndex, pivot);

        quickSort(array, lowIndex, leftPointer - 1);
        quickSort(array, leftPointer + 1, highIndex);
    }

    /* END: QUICK SORT ALGORITHM */

    /* MERGE SORT ALGORITHM */

    private static void mergeSort(int[] array, int left, int right) {
        if(left < right) {
            int mid = (left+right) / 2; // Find the middle element
            mergeSort(array, left, mid); // Sort the first half
            mergeSort(array, mid + 1, right); // Sort the second half
            merge(array, left, mid, right); // Merge the sorted halves
        }
    }

    private static void merge(int[] array, int left, int mid, int right) {
        // Find sizes of two subarrays to be merged
        int n1 = mid - left + 1;
        int n2 = right - mid;

        // Create Temp Arrays
        int[] leftTemp = new int[n1];
        int[] rightTemp = new int[n2];

        // Copy Data to Temp Arrays
        for(int i = 0; i < n1; i++) {
            leftTemp[i] = array[left + i];
        }

        for(int j = 0; j < n2; j++) {
            rightTemp[j] = array[mid + 1 + j];
        }

        // Merge the temp arrays
        // Initial index of merged subarray array
        int i = 0, j = 0, k = left;

        while (i < n1 && j < n2) {
            if (leftTemp[i] <= rightTemp[j]) {
                array[k] = leftTemp[i];
                i++;
            } else {
                array[k] = rightTemp[j];
                j++;
            }

            k++;
        }

        // Copy remaining elements of leftTemp if any
        while (i < n1) {
            array[k] = leftTemp[i];
            i++;
            k++;
        }

        // Copy remaining elements of rightTemp if any
        while (j < n2) {
            array[k] = rightTemp[j];
            j++;
            k++;
        }
    }

    /* END: MERGE SORT ALGORITHM */

    private static void selectionSort(int[] numbers) {
        for(int i = 0; i < numbers.length - 1; i++) {
            int smallest = i;
            // Find the smallest element in unsorted array
            for(int j = i + 1; j < numbers.length; j++) {
                if(numbers[j] < numbers[smallest]) {
                    smallest = j;
                }
            }
            // Swap the smallest element with the first element
            int temp = numbers[smallest];
            numbers[smallest] = numbers[i];
            numbers[i] = temp;
        }
    }

    private static void bubbleSort(int[] numbers) {
        int temp;
        for( int i = 0; i < numbers.length; i++) {
            for(int j = 0; j < numbers.length - 1; j++) {
                if (numbers[j] > numbers[j + 1]) {
                    temp = numbers[j];
                    numbers[j] = numbers[j + 1];
                    numbers[j + 1] = temp;
                }
            }
        }
    }

    private static void insertionSort(int[] numbers, int start, int end) {
        int temp;
        for (int i = start; i < end; i++) {
            for (int j = i; j > start; j--) {
                if (numbers[j] < numbers[j - 1]) {
                    temp = numbers[j];
                    numbers[j] = numbers[j - 1];
                    numbers[j - 1] = temp;
                }
            }
        }
    }
}