class Solution

fun Solution.countUnivalSubtrees(root: TreeNode?): Int {

var ret = 0

fun dfs(node:TreeNode?):Boolean{

if(node==null) return true

val matchLeft = if(node.left==null) true else

dfs(node.left) && node.`val` == node.left.`val`

val matchRight = if(node.right==null) true else

dfs(node.right) && node.`val` == node.right.`val`

if(matchLeft && matchRight){

ret++

return true

}

return false

}

dfs(root)

return ret

}