LeetCode—108. Convert Sorted Array to Binary Search Tree

LeetCode—108. Convert Sorted Array to Binary Search Tree

题目

https://leetcode.com/problems/convert-sorted-array-to-binary-search-tree/description/
将一个递增数组转化为平衡二叉搜索树。平衡二叉搜索树首先是一个二叉搜索树，其次要求每一个节点的左右子树高度差不超过1.

思路及解法

思路很简单。首先构建树，大多数情况是用递归。对于这道题，每次取数组的中间位置的数作为根节点，左侧作为左子树，右侧作为右子树，就OK了。

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