104. Maximum Depth of Binary Tree
https://leetcode.com/problems/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:
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, 104]. -100 <= Node.val <= 100
Problem
Find the deepest node in the tree — what is its depth?
Approach
This problem is similar to 226 Invert Binary Tree, and we’ll also use recursion, but with a different approach.
Treat each node as a root node, declare a depth variable, increment by 1 going down each level and decrement by 1 going up. Traverse all nodes, updating the answer whenever the depth increases. Finally, return the answer.
- Declare global depth and result variables.
- Start recursive traversal — increment the depth variable by 1 when going deeper, decrement by 1 when going back up.
- Treat left and right children as roots, continuing to recursively call the calculateDepth method.
- Whenever depth exceeds the current result, update the result to the current depth.
Source Code
/**
* Definition for a binary tree node.
* type TreeNode struct {
* Val int
* Left *TreeNode
* Right *TreeNode
* }
*/
var depth int
var ans int
func maxDepth(root *TreeNode) int {
depth = 1
ans = 0
calculateDepth(root)
return ans
}
func calculateDepth(root *TreeNode) {
if root == nil {
return
}
if ans < depth {
ans = depth
}
depth++
calculateDepth(root.Left)
calculateDepth(root.Right)
depth--
}
Closing
Do you have a better or simpler solution?
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