Merge Sort

public class Solution {
    /**
     * @param A an integer array
     * @return void
     */
    public void sortIntegers(int[] A) {
        // Write your code here
        if (A == null || A.length == 0) {
            return;
        }
        mergeSort(A, 0, A.length - 1);
    }
    
    private void mergeSort(int[] A, int start, int end) {
        if (start >= end) {
            return;
        }
        int mid = start + (end - start) / 2;
        mergeSort(A, start, mid);
        mergeSort(A, mid + 1, end);
        merge(A, start, mid, end);
    }
    
    private void merge(int[] A, int start, int mid, int end) {
        int[] temp = new int[end - start + 1];
        int i = start;
        int j = mid + 1;
        int k = 0;
        while (i <= mid && j <= end) {
            if (A[i] <= A[j]) {
                temp[k++] = A[i++];
            } else {
                temp[k++] = A[j++];
            }
        }
        while (i <= mid) {
            temp[k++] = A[i++];
        }
        while (j <= end) {
            temp[k++] = A[j++];
        }
        k--;
        while (k >= 0) {
            A[end--] = temp[k--];
        }
    }
}