104. Maximum Depth of Binary Tree

Easy
Given the root of a binary tree, return its maximum depth.
A binary tree's maximum depth is the number of nodes along the longest path from the root node down to the farthest leaf node.
Example 1:
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Input: root = [3,9,20,null,null,15,7]
Output: 3
Example 2:
Input: root = [1,null,2]
Output: 2
Constraints:
  • The number of nodes in the tree is in the range [0, 10^4].
  • -100 <= Node.val <= 100

解題

/**
* Definition for a binary tree node.
* type TreeNode struct {
* Val int
* Left *TreeNode
* Right *TreeNode
* }
*/
func maxDepth(root *TreeNode) int {
if root == nil { return 0 }
return 1 + max(maxDepth(root.Left), maxDepth(root.Right))
}
​
func max(a, b int) int {
if a > b { return a }
return b
}