- https://leetcode.com/problems/convert-sorted-array-to-binary-search-tree/description/
- Given an array where elements are sorted in ascending order, convert it to a height balanced BST.
- For this problem, a height-balanced binary tree is defined as a binary tree in which the depth of the two subtrees of every node never differ by more than 1.
- Example:
- Given the sorted array: [-10,-3,0,5,9],
- One possible answer is: [0,-3,9,-10,null,5], which represents the following height balanced BST:
- 0
- / \
- -3 9
- / /
- -10 5
- time: o(n) space: o(height)
pre order: 先弄自己, 再管下面的兄弟
- public TreeNode sortedArrayToBST(int[] nums) {
- if (nums == null || nums.length == 0) return null;
- int left = 0,
- right = nums.length - 1;
- return helper(nums, left, right);
- }
- //everytime create the root and connect to left and right
- private TreeNode helper(int[] nums, int left, int right) {
- int mid = left + (right - left) / 2;
- TreeNode node = new TreeNode(nums[mid]);
- if (mid + 1 <= right) {
- node.right = helper(nums, mid + 1, right);
- }
- if (mid - 1 >= left) {
- node.left = helper(nums, left, mid - 1);
- }
- //going down and repeat
- return node;
- }
- LC.108.Convert Sorted Array to Binary Search Tree
来源: http://www.bubuko.com/infodetail-2513485.html