104. Maximum Depth of Binary Tree

Description of Problem

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, 10^4].
-100 <= Node.val <= 100

Solution

Tags: Binary Tree Rust

Code (Rust)

// Definition for a binary tree node.
// #[derive(Debug, PartialEq, Eq)]
// pub struct TreeNode {
//   pub val: i32,
//   pub left: Option<Rc<RefCell<TreeNode>>>,
//   pub right: Option<Rc<RefCell<TreeNode>>>,
// }
// 
// impl TreeNode {
//   #[inline]
//   pub fn new(val: i32) -> Self {
//     TreeNode {
//       val,
//       left: None,
//       right: None
//     }
//   }
// }
use std::cmp;
use std::rc::Rc;
use std::cell::RefCell;
impl Solution {
    pub fn max_depth(root: Option<Rc<RefCell<TreeNode>>>) -> i32 {
        match root {
            None => return 0,
            Some(node) => {
                let node = (*node).borrow();
                return 1 + cmp::max(
                    Self::max_depth( node.left.clone() ),
                    Self::max_depth( node.right.clone() ),
                )
            }
        }
    }
}

Code (C++)

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode() : val(0), left(nullptr), right(nullptr) {}
 *     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
 *     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
 * };
 */
class Solution {
public:
    int maxDepth(TreeNode* root) {
        if (root == nullptr){
            return 0;
        }
        else{
            return 1 + std::max( maxDepth(root->left), maxDepth(root->right) );
        }
    }
};

Complexity

n is the number of nodes in the tree
h is the height of the tree

Time complexity:

\( T(n) = O(n) \)

Auxiliary Space:

\( S(n) = O(h) \)

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