[leetcode]108. Convert Sorted Array to Binary Search Tree

题目

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.

解法

思路

经典的二分法思路，每次把中间的那个元素放在根节点，运用递归即可解决问题

代码

/**
 * 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) {
        return helper(nums, 0, nums.length-1);
    }
    public TreeNode helper(int[] nums, int left, int right) {
        if(left > right) return null;
        int mid = (left + right)/2;
        TreeNode root = new TreeNode(nums[mid]);
        root.left = helper(nums, left, mid-1);
        root.right = helper(nums, mid+1, right);
        return root;
    }
}