Category: Interview

  private static void selectionSort(int[] arr) {
        int n = arr.length;
        for (int i = 0; i < n; i++) {
            int minIndex = i;
            for (int j = i + 1; j < n; j++) {
                if (arr[j] < arr[minIndex]) {
                    minIndex = j;
                }
            }
//optimisation used :  outer loop used for swapping - internal for index tracking
            int temp = arr[minIndex];
            arr[minIndex] = arr[i];
            arr[i] = temp;

        }
    }

  private static void bubbleSort(int[] arr) {
        int n = arr.length;
        for (int i = 0; i < n - 1; i++) {

            for (int j = 0; j < n - 1; j++) {
                if(arr[j]>arr[j+1]){
                    int temp=arr[j+1];
                    arr[j+1]=arr[j];
                    arr[j]=temp;
                }
            }
        }
     
    }

 public static void insertionSort(int[] arr) {
        int n = arr.length;
        for (int i = 1; i < n; i++) {
            int key = arr[i];
            int j = i - 1;
            // Move elements of arr[0..i-1] that are greater than key to one position ahead
            while (j >= 0 && arr[j] > key) {
                arr[j + 1] = arr[j];
                j = j - 1;
            }
            arr[j + 1] = key;
        }
    }

  public static void quickSort(int[] arr, int low, int high) {
        if (low < high) {
            int pi = partition(arr, low, high);
            quickSort(arr, low, pi - 1);  // Recursively sort elements before partition
            quickSort(arr, pi + 1, high); // Recursively sort elements after partition
        }
    }

    private static int partition(int[] arr, int low, int high) {
        int pivot = arr[high];
        int i = (low - 1); // Index of smaller element
        for (int j = low; j < high; j++) {
            if (arr[j] < pivot) {
                i++;
                // Swap arr[i] and arr[j]
                int temp = arr[i];
                arr[i] = arr[j];
                arr[j] = temp;
            }
        }
        // Swap arr[i+1] and arr[high] (or pivot)
        int temp = arr[i + 1];
        arr[i + 1] = arr[high];
        arr[high] = temp;

        return i + 1;
    }

public class MergeSort {
    public static void mergeSort(int[] arr, int left, int right) {
        if (left < right) {
            int middle = (left + right) / 2;
            // Sort first and second halves
            mergeSort(arr, left, middle);
            mergeSort(arr, middle + 1, right);
            // Merge the sorted halves
            merge(arr, left, middle, right);
        }
    }

    private static void merge(int[] arr, int left, int middle, int right) {
        int n1 = middle - left + 1;
        int n2 = right - middle;

        // Temporary arrays
        int[] L = new int[n1];
        int[] R = new int[n2];

        // Copy data to temp arrays
        for (int i = 0; i < n1; i++)
            L[i] = arr[left + i];
        for (int j = 0; j < n2; j++)
            R[j] = arr[middle + 1 + j];

        // Merge the temp arrays
        int i = 0, j = 0;
        int k = left;
        while (i < n1 && j < n2) {
            if (L[i] <= R[j]) {
                arr[k] = L[i];
                i++;
            } else {
                arr[k] = R[j];
                j++;
            }
            k++;
        }

        // Copy remaining elements of L[]
        while (i < n1) {
            arr[k] = L[i];
            i++;
            k++;
        }

        // Copy remaining elements of R[]
        while (j < n2) {
            arr[k] = R[j];
            j++;
            k++;
        }
    }

    public static void main(String[] args) {
        int[] arr = {12, 11, 13, 5, 6, 7};
        
        // Call mergeSort with the full range of the array
        mergeSort(arr, 0, arr.length - 1);
        
        // Print the sorted array
        System.out.println("Sorted array:");
        for (int num : arr) {
            System.out.print(num + " ");
        }
    }
}