[LintCode] Maximum Depth of Binary Tree 二叉树的最大深度

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.

Have you met this question in a real interview? 

Yes

Example

Given a binary tree as follow:

  1
 /  
2   3
   / 
  4   5

The maximum depth is 3.

LeetCode上的原题，请参见我之前的博客Maximum Depth of Binary Tree。

解法一：

class Solution {
public:
    /**
     * @param root: The root of binary tree.
     * @return: An integer
     */
    int maxDepth(TreeNode *root) {
        if (!root) return 0;
        return 1 + max(maxDepth(root->left), maxDepth(root->right));
    }
};

解法二：

class Solution {
public:
    /**
     * @param root: The root of binary tree.
     * @return: An integer
     */
    int maxDepth(TreeNode *root) {
        if (!root) return 0;
        int res = 0;
        queue<TreeNode*> q;
        q.push(root);
        while(!q.empty()) {
            ++res;
            int n = q.size();
            for (int i = 0; i < n; ++i) {
                TreeNode *t = q.front(); q.pop();
                if (t->left) q.push(t->left);
                if (t->right) q.push(t->right);
            }
        }
        return res;
    }
};