173.二叉搜索树迭代器

/**
 * 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 {TreeNode} root
 */
var BSTIterator = function (root) {
    this.root = root

    let nodes = []
    const inorder = (root) => {
        if(!root) {
            return
        }
        // 左中右
        inorder(root.left)
        nodes.push(root.val)
        inorder(root.right)
    }
    inorder(this.root)

    this.nodes = nodes
    this.curIndex = -1
};

/**
 * @return {number}
 */
BSTIterator.prototype.next = function () {
    this.curIndex++
    return this.nodes[this.curIndex]
};

/**
 * @return {boolean}
 */
BSTIterator.prototype.hasNext = function () {
    if (this.curIndex < this.nodes.length - 1) {
        return true
    }
    return false
};

/**
 * Your BSTIterator object will be instantiated and called as such:
 * var obj = new BSTIterator(root)
 * var param_1 = obj.next()
 * var param_2 = obj.hasNext()
 */