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
/** * Definition for a binary tree node. * public class TreeNode { * int val; * TreeNode left; * TreeNode right; * TreeNode(int x) { val = x; } * } */ class Solution { public TreeNode sortedArrayToBST(int[] nums) { if(nums.length == 0) return null; return help(nums,0, nums.length - 1); } public TreeNode help(int[] nums, int start, int end){ if(end < start) return null; int rootind = (end + start) / 2; TreeNode root = new TreeNode(nums[rootind]); root.left = help(nums, start, rootind - 1); root.right = help(nums, rootind + 1, end); return root; } }
没什么特殊的,每一步都是把中间的当作root,然后两边作为subtree。
递归终止条件是end<start,因为存在==的情况(单一node)