Contents.swift

//: Playground - noun: a place where people can play

import UIKit

var str = "Hello, playground"


//https://docs.google.com/document/d/1te7mLS06MEYwETFSbVBqMrIzJ43GTEo5uuCiWdB0fyE/edit?usp=drivesdk


//1


//Bonus1


//Bonus2

//Homework
//
//Using the Swift binary tree implementation below (the Node class), implement a function that takes in a string containing a simple postfix mathematical expression, and returns a binary tree representing that expression using the process described here.
//
//Required: Build and return the binary tree representation of the expression. The following characters should be treated as operators: +-*/
//
//Bonus 1: Print the inorder traversal of the binary tree.
//Bonus 2: Evaluate the expression (substituting integers for the letters in the expression).
//
//Tips:
//You may use additional data structures—as suggested in the link above, you will at least want to use a stack. This can be done using the Array type in Swift.
//Test your tree by checking to see if the string returned by postorderDescription is equal to the input string.
//
//Sample input:
//"ab+cde+**"
//
//Template for the function you should implement:
//func parseExpression(input: String) -> Node<Character>? {
//    // Your implementation here!
//    let operators: Set<Character> = ["+", "-", "*", "/"]
//    var stack: [Node<Character>] = []
//    for character in input.characters {
//        // Do something for each character
//    }
//    return nil
//}
//
//Binary tree implementation:
//class Node<T> {
//    let value: T
//    var left: Node?
//    var right: Node?
//    init(value: T) {
//        self.value = value
//    }
//}
//
//extension Node: CustomStringConvertible {
//    var description: String {
//        return "\(value)"
//    }
//    var postorderDescription: String {
//        let lt = left?.postorderDescription ?? ""
//        let rt = right?.postorderDescription ?? ""
//        return lt + rt + description
//    }
//}