Evaluating an arithmetic expression from a binary tree

Question

Let's say I have a Binary Tree that looks like

        +
    2       *
          5   8    

I've written a function to traverse inorder to solve it as 2+5*8

Is there a better way? Using eval seems a bit hacky and perhaps I can just have a function calculate the total sum on either side and then do a left + right instead.

class Node {
  constructor(value) {
    this.value = value;
    this.left = null;
    this.right = null;
  }
}

class BinarySearchTree {
  constructor() {
    this.root = null;
  }
  
  solveEquation() {
    let equation = "";
    let traverse = (currentNode = this.root) => {      
      if (currentNode !== null) {
        if (currentNode.left !== null) traverse(currentNode.left);
        equation += currentNode.value;
        if (currentNode.right !== null) traverse(currentNode.right);
      }
    }
    
    traverse();
    return eval(equation);
  }

  init() {
    this.root = new Node('+');
    let currentNode = this.root;
    currentNode.left = new Node(2);
    currentNode.right = new Node('*');
    currentNode = currentNode.right;
    currentNode.left = new Node(5);
    currentNode.right = new Node(8);
  }
}

let bst = new BinarySearchTree();
bst.init();
console.log(bst.solveEquation());

Answer 1

This is not a search tree. You can call it an abstract syntax tree, or just a binary tree.

You can use a dispatch table to evaluate ops.

 dispatch = {
      '+': (a,b) => a+b,
      '*': (a,b) => a*b
 }
 ...
 if (node.left && node.right && node.value in dispatch) dispatch[node.value]( traverse(node.left), traverse(node.right) );