# leetcode\_104

## 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

1. **recursion(dfs)**

```cpp
/**
 * 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 max(maxDepth(root->left), maxDepth(root->right)) + 1;
    }
};
```

1. **iteration(dfs/bfs)**