import java.util.Arrays;

public class MergeSort_Algo_merge {
    public static void main(String[] args)
    {
        int[] ary001_sorted = new int[] {9, 20, 100, 300};
        int[] ary002_sorted = new int[] {3, 10, 11, 201};
        int[] merge = merge(ary001_sorted, ary002_sorted);
        printArray(merge);
    }

    // imagine you are at the last step of mergesort when you are coming from the bottom up.
    // Therefore, the array with size 1 is sorted; then up and the arrays with size 2 will be sorted too.
    // Here, we are simulating a up-k layers, and now we have two sorted sub-arrays to be merged.
    private static int[] merge(int[] aryLeft, int[] aryRight){
        if (aryLeft.length == 0) return aryRight;
        if (aryRight.length == 0) return aryLeft;

        int[] result = null;
        if (aryLeft[0] <= aryRight[0]) { // if smaller, extract it out in this layer
            result = concat(subArray(aryLeft, 0, 1) , merge(subArray(aryLeft, 1, aryLeft.length), aryRight)) ;
        }else {
            result = concat(subArray(aryRight, 0, 1) , merge(aryLeft, subArray(aryRight, 1, aryRight.length))) ;
        }
        return result;
    }


    private static int[] concat(int[] first, int[] second){
        int[] both = Arrays.copyOf(first, first.length + second.length);
        System.arraycopy(second, 0, both, first.length, second.length);
        return both;
    }

    private static int[] copyArray(int[] array){
        return subArray(array, 0, array.length);
    }

    public static int[] subArray(int[] array, int beg, int end) {
        return Arrays.copyOfRange(array, beg, end);
    }

    private static void printArray(int[] ary){
        for (int i = 0; i < ary.length; i++) {
            System.out.printf("%4d" , ary[i]);
        }
        System.out.println();
    }
    private static void print2DArray(int[][] ary){
        for (int i = 0; i < ary.length; i++) {
            for (int j = 0; j < ary[i].length; j++) {
                System.out.printf("%4d" , ary[i][j]);
            }
            System.out.println();
        }
    }
}