Code Quiz

Buggy BST Insert

Spot the subtle recursion bug that silently drops nodes in a binary search tree insert.

Codejavascript

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

// Unlike a heap-backed priority queue (which only tracks min/max),
// a BST keeps ALL keys ordered so we can do lookups by value.
function insert(root, val) {
  if (root === null) return new Node(val);

  if (val < root.val) {
    insert(root.left, val);
  } else {
    insert(root.right, val);
  }

  return root;
}

let tree = null;
tree = insert(tree, 50);
insert(tree, 30);
insert(tree, 70);
insert(tree, 20);
// Expected in-order: 20, 30, 50, 70

What is the bug that causes inserted values (20, 30, 70) to be lost?

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