1448. Count Good Nodes in Binary Tree

Given a binary tree root, a node X in the tree is named good if in the path from root to X there are no nodes with a value greater than X.

Return the number of good nodes in the binary tree.

Example 1:

Input: root = [3,1,4,3,null,1,5]
Output: 4
Explanation: Nodes in blue are **good**.
Root Node (3) is always a good node.
Node 4 -> (3,4) is the maximum value in the path starting from the root.
Node 5 -> (3,4,5) is the maximum value in the path
Node 3 -> (3,1,3) is the maximum value in the path.

Example 2:

Input: root = [3,3,null,4,2]
Output: 3
Explanation: Node 2 -> (3, 3, 2) is not good, because "3" is higher than it.

Example 3:

Input: root = [1]
Output: 1
Explanation: Root is considered as **good**.

Constraints:

• The number of nodes in the binary tree is in the range [1, 10^5].
• Each node's value is between [-10^4, 10^4].

# @lc code=start
using LeetCode

function good_nodes(root::TreeNode)::Int
    dfs(::Nothing, args...) = 0
    function dfs(n::TreeNode, mval::Int)::Int
        res = 0
        (n.val >= mval) && (res += 1)
        n_max = max(mval, n.val)
        res += dfs(n.left, n_max)
        res += dfs(n.right, n_max)
        return res
    end
    return dfs(root, typemin(Int))
end
# @lc code=end

good_nodes (generic function with 1 method)

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