Find Bottom Left Tree Value

Description

Given a binary tree, find the leftmost value in the last row of the tree.

Example 1:

Input:
2

/ 

1   3
Output:
1

Example 2:

Input:
    1
   / \
  2   3
 /   / \
4   5   6
   /
  7

Output:
7

Note: You may assume the tree (i.e., the given root node) is not NULL.

Solution(javascript)

/*
 * @lc app=leetcode id=513 lang=javascript
 *
 * [513] Find Bottom Left Tree Value
 *
 * https://leetcode.com/problems/find-bottom-left-tree-value/description/
 *
 * algorithms
 * Medium (57.65%)
 * Total Accepted:    64.4K
 * Total Submissions: 111.3K
 * Testcase Example:  '[2,1,3]'
 *
 *
 * Given a binary tree, find the leftmost value in the last row of the tree.
 *
 *
 * Example 1:
 *
 * Input:
 *
 * ⁠   2
 * ⁠  / \
 * ⁠ 1   3
 *
 * Output:
 * 1
 *
 *
 *
 * ⁠ Example 2:
 *
 * Input:
 *
 * ⁠       1
 * ⁠      / \
 * ⁠     2   3
 * ⁠    /   / \
 * ⁠   4   5   6
 * ⁠      /
 * ⁠     7
 *
 * Output:
 * 7
 *
 *
 *
 * Note:
 * You may assume the tree (i.e., the given root node) is not NULL.
 *
 */
/**
 * Definition for a binary tree node.
 * function TreeNode(val) {
 *     this.val = val;
 *     this.left = this.right = null;
 * }
 */
/**
 * @param {TreeNode} root
 * @return {number}
 */
const findBottomLeftValue = (root) => {
  let frontier = [root]
  let previous = frontier
  while (frontier.length) {
    const next = []
    frontier.forEach((node) => {
      if (node.left) {
        next.push(node.left)
      }
      if (node.right) {
        next.push(node.right)
      }
    })
    if (next.length !== 0) {
      previous = next
    }
    frontier = next
  }
  return previous[0].val
}