104. Maximum Depth of Binary Tree

• Difficulty: Easy

• Topics: Tree, Depth-first Search

• Similar Questions:

  • Balanced Binary Tree

  • Minimum Depth of Binary Tree

  • Maximum Depth of N-ary Tree

Problem:

Given a binary tree, find its maximum depth.

The maximum depth is the number of nodes along the longest path from the root node down to the farthest leaf node.

Note: A leaf is a node with no children.

Example:

Given binary tree [3,9,20,null,null,15,7],

    3
   / \
  9  20
    /  \
   15   7

return its depth = 3.

Solutions:

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