分治-归并系列一＞归并排序

题目：

链接: link

解析：

代码：

//归并：
    int[] tmp;
    public int[] sortArray(int[] nums) {
        tmp = new int[nums.length];
        sortArray(nums,0,nums.length-1);
        return nums;
    }

    public void sortArray(int[] nums, int left, int right){
        if(left >= right) return;

        int mid = (left+right)/2;
        // 1. 根据中间点划分区间:[left,mid][mid+1,right]
        sortArray(nums, left,mid);
        sortArray(nums,mid+1,right);

        //合并两个有序数组：
        int cur1 = left, cur2 = mid+1,i = 0;
        while(cur1 <= mid && cur2 <= right)
            tmp[i++] = nums[cur1] <= nums[cur2] ? nums[cur1++] : nums[cur2++];

        while(cur1 <= mid) tmp[i++] = nums[cur1++];
        while(cur2 <= right) tmp[i++] = nums[cur2++];

        //把排序好的数组放到原数组里
        for(int j = left; j <= right; j++){
            nums[j] = tmp[j-left];
        }
    }