合并排序算法

Question

i have been solving the problem related to merge sorting but dont know what is the problem in my program so can you please look on it?

the question was to give a unsorted array and it will provide sorted without changing the original array. please let me know where is my mistake

public static int []  mergeSort(int[] in){

        int [] temp = in.clone();

        if (temp.length <= 1){

            }


        else{
            int [] first = new int[temp.length/2];
            int [] second = new int [temp.length - first.length];

            for (int i=0; i<first.length; i++){
                first[i] = temp[i];
            }

            for (int i = 0; i < second.length; i++){
                second[i] = temp[first.length+i];
            }

            mergeSort(first);
            mergeSort(second);
            merg(first,second,temp);

        }

    return temp;
    }
    public static void merg(int [] first, int[] second, int []newTemp){


        int i =0;
        int j = 0;
        int k = 0;
        while(i <first.length && j < second.length ){

            if(first[i] <=second[j]){

                newTemp[k] = first[i];
                i++;
            }
            else{
                newTemp[k] = second[j];
                j++;

            }
            k++;

        }
        while (i < first.length){
            newTemp[k] = first[i];
            i++;
            k++;
        }
        while(j < second.length){
            newTemp[k]= second[j];
            j++;
            k++;
        }

    }

Answer 1

The problem is because you are cloning the array and each time you call the mergeSort() function, it again clones the array. It needs to be cloned only the first time function is called.

Here is the complete solution for your problem. You should call the first mergeSort() function.

public static int[] mergeSort(int[] in) {
    return mergeSort(in, 0);
}

public static int[] mergeSort(int[] in, int number_of_times_called) {

    int[] temp;
    if (number_of_times_called == 0)
        temp = in.clone();
    else
        temp = in

    if (temp.length <= 1){
        return temp;
    }


    else{
        int [] first = new int[temp.length/2];
        int [] second = new int [temp.length - first.length];

        for (int i=0; i<first.length; i++){
            first[i] = temp[i];
        }

        for (int i = 0; i < second.length; i++){
            second[i] = temp[first.length+i];
        }

        mergeSort(first);
        mergeSort(second);
        merg(first,second,temp);

    }

    return temp;
}

public static void merg(int [] first, int[] second, int []newTemp){


    int i =0;
    int j = 0;
    int k = 0;
    while(i <first.length && j < second.length ){

        if(first[i] <=second[j]){

            newTemp[k] = first[i];
            i++;
        }
        else{
            newTemp[k] = second[j];
            j++;

        }
        k++;

    }
    while (i < first.length){
        newTemp[k] = first[i];
        i++;
        k++;
    }
    while(j < second.length){
        newTemp[k]= second[j];
        j++;
        k++;
    }

}