Univalued Binary Tree

Description

A binary tree is univalued if every node in the tree has the same value.

Return true if and only if the given tree is univalued.

 

Example 1:

Input: [1,1,1,1,1,null,1]
Output: true

Example 2:

Input: [2,2,2,5,2]
Output: false

 

Note:

1. The number of nodes in the given tree will be in the range [1, 100].
2. Each node's value will be an integer in the range [0, 99].

Solution(javascript)

/**
 * Definition for a binary tree node.
 * function TreeNode(val) {
 *     this.val = val;
 *     this.left = this.right = null;
 * }
 */
/**
 * @param {TreeNode} root
 * @return {boolean}
 */
const isUnivalTree = function (root) {
  const aux = (node, prev) => {
    if (!node) {
      return true
    }
    if (node.val !== prev) {
      return false
    }
    let isLeftValid = true
    let isRightValid = true
    if (node.left) {
      isLeftValid = aux(node.left, prev)
    }

    if (isLeftValid && node.right) {
      isRightValid = aux(node.right, prev)
    }
    return isLeftValid && isRightValid
  }
  if (!root) {
    return true
  }
  return aux(root, root.val)
}