Leetcode Convert Sorted Array to Binary Search Tree

最新推荐文章于 2022-02-19 22:56:38 发布

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本文介绍了一种将已排序的数组转换为高度平衡的二叉搜索树的方法。通过递归方式选取中间元素作为根节点，并继续处理左右子数组以确保树的平衡性。

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Given an array where elements are sorted in ascending order, convert it to a height balanced BST.

Difficulty: Medium

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
public class Solution {
    public TreeNode helper(int[] nums, int begin, int end){
        if(end < begin) return null;
        if(begin == end) return (new TreeNode(nums[begin]));
        if(end - begin == 1){
            TreeNode root = new TreeNode(nums[begin]);
            root.right = helper(nums, end, end);
            return root;
        }
        int mid = (end - begin)/2 + begin;
        TreeNode root = new TreeNode(nums[mid]);
        root.left = helper(nums, begin, mid - 1);
        root.right = helper(nums, mid + 1, end);
        return root;
        
    }
    public TreeNode sortedArrayToBST(int[] nums) {
        if(nums.length == 0) return null;
        return helper(nums, 0, nums.length - 1);
    }
}