Count Univalue Subtrees

Description

null

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 countUnivalSubtrees = function (root) {
  const aux = (node) => {
    if (!node) {
      return [true, null, 0]
    }
    const [leftValid, leftVal, count1] = aux(node.left)
    const [rightValid, rightVal, count2] = aux(node.right)
    const { val } = node
    const count = count1 + count2
    if (leftValid && rightValid) {
      if (leftVal === null && rightVal === null) {
        return [true, val, count + 1]
      }
      if (leftVal === null || rightVal === null) {
        if (val === (leftVal === null ? rightVal : leftVal)) {
          return [true, val, count + 1]
        }
        return [false, val, count]
      }
      if (leftVal === val && rightVal === val) {
        return [true, val, count + 1]
      }
      return [false, val, count]
    }
    return [false, val, count]
  }
  return aux(root)[2]
}