leetcode学习笔记18

108. Convert Sorted Array to Binary Search Tree

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.

class Solution {
    public TreeNode sortedArrayToBST(int[] nums) {
        return helper(nums,0,nums.length-1);
    }
    public TreeNode helper(int[] nums,int start,int end) {
    	if(start>end)
    		return null;
    	int len=end-start+1;
        TreeNode root = new TreeNode(nums[start+len/2]);
        root.left=helper(nums,start,start+len/2-1);
        root.right=helper(nums,start+len/2+1,end);
        return root;
    }
}