1448-count-good-nodes-in-binary-tree.swift

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 * public var val: Int
 * public var left: TreeNode?
 * public var right: TreeNode?
 * public init() { self.val = 0; self.left = nil; self.right = nil; }
 * public init(_ val: Int) { self.val = val; self.left = nil; self.right = nil; }
 * public init(_ val: Int, _ left: TreeNode?, _ right: TreeNode?) {
 * self.val = val
 * self.left = left
 * self.right = right
 * }
 * }
 */
classSolution{
varglobalCount:Int=0

func goodNodes(_ root:TreeNode?)->Int{
self.globalCount =0
visit(root, maxSoFar:nil)
returnself.globalCount
}
}

privateextensionSolution{
 // DFS/Recursive traversal
func visit(_ node:TreeNode?, maxSoFar:Int?)->Void{
 // Base case 1. Node is nil
guardlet node = node else{return}

 // Base case 2. Initial value doesn't exist (in case of root)
letmaxVal:Int
iflet maxSoFar = maxSoFar {
 maxVal =max(maxSoFar, node.val)
}else{
 maxVal = node.val
}

 // update global count
if !(maxVal > node.val){
self.globalCount +=1
}

 // visit children
visit(node.left, maxSoFar: maxVal)
visit(node.right, maxSoFar: maxVal)
}
}