Problem

Find the sum of all left leaves in a given binary tree.

Example:

    3
   / \
  9  20
    /  \
   15   7

There are two left leaves in the binary tree, with values 9 and 15 respectively. Return 24.

Pre analysis

Will take recursive approach

Another solution

function sumOfLeftLeaves(root) {
  let sum = 0;
  let queue = [root];

  while (queue.length) {
    let currNode = queue.shift();
    if (!currNode) continue;

    if (currNode.left) {
      if (isLeafNode(currNode.left) === true) sum += currNode.left.val;
      queue.push(currNode.left);
    }
    if (currNode.right) {
      queue.push(currNode.right);
    }
  }

  return sum;
};

function isLeafNode(node) {
  return !node.left && !node.right;
};