Find Largest Value in Each Tree Row

Description

Given the root of a binary tree, return an array of the largest value in each row of the tree (0-indexed).

 

 

Example 1:

Input: root = [1,3,2,5,3,null,9]
Output: [1,3,9]

Example 2:

Input: root = [1,2,3]
Output: [1,3]

Example 3:

Input: root = [1]
Output: [1]

Example 4:

Input: root = [1,null,2]
Output: [1,2]

Example 5:

Input: root = []
Output: []

 

Constraints:

• The number of nodes in the tree will be in the range [0, 104].
• -231 <= Node.val <= 231 - 1

Solution(javascript)

/**
 * Definition for a binary tree node.
 * function TreeNode(val) {
 *     this.val = val;
 *     this.left = this.right = null;
 * }
 */
/**
 * @param {TreeNode} root
 * @return {number[]}
 */
const largestValues = (root) => {
  const res = []
  if (!root) {
    return res
  }
  let frontier = [root]
  while (frontier.length) {
    const next = []
    let max = -Infinity
    frontier.forEach((node) => {
      if (node.val > max) {
        max = node.val
      }
      if (node.left) {
        next.push(node.left)
      }
      if (node.right) {
        next.push(node.right)
      }
    })
    frontier = next
     res.push(max)
  }
  return res
}