Depth-first-search - Easy Level - Question 1

Depth-first-search - Easy Level - Question 1

Leetcode104. Maximum Depth of Binary Tree

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.

Constraints:

The number of nodes in the tree is in the range [0, 10^4].

-100 <= Node.val <= 100

Analysis:

A binary tree has a recursive structure in nature: the left child is the root of the sub binary tree on the left; the right child is the root of the sub binary tree on the right.

So we can apply DFS to this question: 

1. the base cases: if the node is null, return 0; if not

2. the maximum depth should be 1 + max(Maximum Depth of the left sub tree, Maximum Depth of the right sub tree).

See the code below:

/**
 * 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) return 0;
        return 1 + max(maxDepth(root->left), maxDepth(root->right));
    }
};

Note: pay attention to the definition of the TreeNode, which can be used when need to write your own struct (for example, in the Trie)

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