Find the In-Order Successor of a node in a BST.

InorderSuccessor.js

class Stack {
    constructor(root) {
        this.stack = []
        while (root) {
            this.stack.push(root)
            root = root.left
        }
    }
    
    hasNext() {
        return this.stack.length > 0
    }
    
    next(preload) {
        var nextNode = this.stack.pop()
        if (preload && nextNode && nextNode.right) {
            var temp = nextNode.right
            while(temp) {
                this.stack.push(temp)
                temp = temp.left
            }
        }
        return nextNode
    }
}

/**
 * Definition for a binary tree node.
 * function TreeNode(val) {
 *     this.val = val;
 *     this.left = this.right = null;
 * }
 */
/**
 * @param {TreeNode} root
 * @param {TreeNode} p
 * @return {TreeNode}
 */
var inorderSuccessor = function(root, p) {
    var stack = new Stack(root)
    while(stack.hasNext()) {
        if (stack.next(true).val === p.val) {
            break
        }
    }
    var returnValue = stack.next(false)
    if (returnValue === undefined) {
        return null
    } else {
        return returnValue
    }
};