归并排序

归并排序

class Solution2 {
    public int[] sortArray(int[] nums) {
        if (nums == null || nums.length == 0) return nums;
        int[] temp = new int[nums.length];
        mergeSort(nums, 0, nums.length - 1, temp);
        return nums;
    }

    private void mergeSort(int[] nums, int start, int end, int[] temp) {
        if (start >= end) {
            return;
        }
        mergeSort(nums, start, (start + end) / 2, temp);
        mergeSort(nums, (start + end) / 2 + 1, end, temp);
        merge(nums, start, (start + end) / 2, end, temp);
    }

    private void merge(int[] nums, int start, int middle, int end, int[] temp) {
        int leftStart=start, rightStart=middle+1;
        int index=start;
        while (leftStart<=middle && rightStart<=end){
            if(nums[leftStart]<=nums[rightStart]) {
                temp[index++]=nums[leftStart++];
            }else {
                temp[index++]=nums[rightStart++];
            }
        }
        while (leftStart<=middle) {
            temp[index++]=nums[leftStart++];
        }
        while (rightStart<=end++) {
            temp[index++]=nums[rightStart++];
        }
        for(int i=start; i<=end; i++) {
            nums[i]=temp[i];
        }
    }

}