【算法】Java实现归并排序

时间复杂度O(nlogn)

    public void mergeSort(int[] nums, int l, int r) {
        if (l >= r) return;
        int mid = (l + r) >> 1; // 取中值点
        mergeSort(nums, l, mid);
        mergeSort(nums, mid + 1, r);
        merge(nums, l, mid, r);
    }

    
    void merge(int[] nums, int left, int mid, int right) {
        int[] temp = new int[right - left + 1];
        int i = left, j = mid + 1;

        // 合并
        for (int k = 0; k < temp.length; k++) {
            // 谁小要谁，i在范围内或者j出界
            if (j > right || (i <= mid && nums[i] <= nums[j])) {
                temp[k] = nums[i++];
            } else {
                temp[k] = nums[j++];
            }
        }
        // 复制到nums
        for (int k = 0; k < temp.length; k++) {
            nums[left + k] = temp[k];
        }
    }