Leetcode - 108 . Convert Sorted Array to Binary Search Tree

 

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Convert Sorted Array to Binary Search Tree - LeetCode

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문제

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

 

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균형 이진 탐색 트리를 만드는 문제이다. 

 

[이진 탐색 트리]

균형 이진 탐색 트리(AVL 트리)

재귀로 푼다.

 

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