javasortingrecursioninsertion-sort

Java recursive insertion sort?


So I am trying to make the following code into a recursive method, insertion sort, but for as much as I try I cannot. Can anyone help me?

public static void insertionSort(int[] array){
    for (int i = 1; i < array.length; i++){
        int j = i;
        int B = array[i];
        while ((j > 0) && (array[j-1] > B)){
            array[j] = array[j-1];
            j--;
        }
        array[j] = B;
    }
}

EDIT: I was thinking of something like this, but it doesn't look very recursive to me...

public static void insertionSort(int[] array, int index){
    if(index < array.length){
        int j = index;
        int B = array[index];
        while ((j > 0) && (array[j-1] > B)){
            array[j] = array[j-1];
            j--;
        }
        array[j] = B;
        insertionSort(array, index + 1);
    }
}

Solution

  • Try this:

    public class RecursiveInsertionSort {
        static int[] arr = {5, 2, 4, 6, 1, 3};
        int maxIndex = arr.length;
    
        public static void main(String[] args) {
            print(arr);
            new RecursiveInsertionSort().sort(arr.length);
        }
    
        /*
          The sorting function uses 'index' instead of 'copying the array' in each    
          recursive call to conserve memory and improve efficiency.
        */
        private int sort(int maxIndex) {
            if (maxIndex <= 1) {
                // at this point maxIndex points to the second element in the array.
                return maxIndex;
            }
    
            maxIndex = sort(maxIndex - 1);  // recursive call
    
            // save a copy of the value in variable 'key'.
            // This value will be placed in the correct position
            // after the while loop below ends.
            int key = arr[maxIndex];  
    
            int i = maxIndex - 1;
    
            // compare value in 'key' with all the elements in array 
            // that come before the element key. 
            while ((i >= 0) && (arr[i] > key)) {
                arr[i+1] = arr[i];
                i--;
            }
            arr[i+1] = key;
            print(arr);
            return maxIndex + 1;
        }
    
        // code to print the array on the console.
        private static void print(int[] arr) {
            System.out.println();
            for (int i : arr) {
                System.out.print(i + ", ");
            }
        }
    }