CODEWITHSUNDEEP
algorithmbinary-search-tree
Jessica
Jessica

Reputation: 594

Binary Search Tree using the find method

I am trying to use the find() method for BST. However, I am encountering errors when I place the 'if' statement incorrectly. When I swap the following 2 lines, my code gave me an error TypeError: Cannot read properties of null (reading 'val'). However, if I used a "else if" for the second statement, it works. Not sure why.

      if (val > current.val) current = current.right // these 2 lines were swapped which gave an error
      if (val < current.val) current = current.left  // these 2 lines were swapped which gave an error

Below is the full code.

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

class BST {
  constructor() {
    this.root = null;
  }

  insert(val) {
    let newNode = new Node(val)
    if (!this.root) {
      this.root = newNode
      return this;
    }

    let current = this.root
    while (true) {
      if (val === current.val) return undefined
      if (val < current.val) {
        if (current.left === null) {
          current.left = newNode
          return this;
        } else {
          current = current.left
        }
      }
      if (val > current.val) {
        if (current.right === null) {
          current.right = newNode
          return this;
        } else {
          current = current.right
        }
      }
    }
  }

  find(val) {
    if (!this.root) return false

    let current = this.root
    while (current) {
      if (val === current.val) return true
      console.log(current.val)
      if (val > current.val) current = current.right // these 2 lines were swapped
      if (val < current.val) current = current.left  // these 2 lines were swapped
    }
    return false
  }
}

let tree = new BST();
console.log(tree.insert(10));
console.log(tree.insert(5));
console.log(tree.insert(13));
console.log(tree.insert(11));
console.log(tree.insert(2));
console.log(tree.insert(16));
console.log(tree.insert(7));

console.log(tree.find(333))

Upvotes: 0

Views: 257

Answers (1)

JackRaBeat
JackRaBeat

Reputation: 489

Because you ask on your second "if" about the current.val but on the first "if" you change the current to null (when you got to the end of the tree), this is why you should use "else if" or to ask if the current == null before you ask about it again.

Notice that if you swap between the lines it won't solve the problem, just transfer the exception to the cases when you have an item that is smaller than any other element in the tree.

Upvotes: 2

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