108. Convert Sorted Array to Binary Search Tree

[Tcdian]

108. Convert Sorted Array to Binary Search Tree

将一个按照升序排列的有序数组，转换为一棵高度平衡二叉搜索树。

本题中，一个高度平衡二叉树是指一个二叉树每个节点 的左右两个子树的高度差的绝对值不超过 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

[Tcdian]

Solution

• JavaScript Solution

/**
 * Definition for a binary tree node.
 * function TreeNode(val, left, right) {
 *     this.val = (val===undefined ? 0 : val)
 *     this.left = (left===undefined ? null : left)
 *     this.right = (right===undefined ? null : right)
 * }
 */
/**
 * @param {number[]} nums
 * @return {TreeNode}
 */
var sortedArrayToBST = function(nums) {
    return buildBST(0, nums.length - 1);

    function buildBST(left, right) {
        if (left > right) {
            return null;
        }
        const mid = (left + right) >> 1;
        const node = new TreeNode(nums[mid]);
        node.left = buildBST(left, mid - 1);
        node.right = buildBST(mid + 1, right);
        return node;
    }
};