Maximum Depth of Binary Tree

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.

Analyse: The same as Minimum Depth of Binary Tree.

1. Recursion

Runtime: 8ms.

 1 /**
 2  * Definition for a binary tree node.
 3  * struct TreeNode {
 4  *     int val;
 5  *     TreeNode *left;
 6  *     TreeNode *right;
 7  *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 8  * };
 9  */
10 class Solution {
11 public:
12     int maxDepth(TreeNode* root) {
13         if(!root) return 0;
14         
15         int leftDepth = maxDepth(root->left);
16         int rightDepth = maxDepth(root->right);
17         
18         if(leftDepth == 0 && rightDepth == 0) return 1;
19         if(leftDepth == 0) leftDepth = INT_MIN;
20         if(rightDepth == 0) rightDepth = INT_MIN;
21         
22         return 1 + max(leftDepth, rightDepth);
23     }
24 };

2. Iteration: Compute the number of level. Initialize the level to be 0, after dealing with the current level, then level++.

Runtime: 8ms.

 1 /**
 2  * Definition for a binary tree node.
 3  * struct TreeNode {
 4  *     int val;
 5  *     TreeNode *left;
 6  *     TreeNode *right;
 7  *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 8  * };
 9  */
10 class Solution {
11 public:
12     int maxDepth(TreeNode* root) {
13         if(!root) return 0;
14         
15         queue<TreeNode* > qu;
16         qu.push(root);
17         int level = 0;
18         while(!qu.empty()){
19             int n = qu.size();
20             while(n--){
21                 TreeNode* current = qu.front();
22                 qu.pop();
23                 
24                 if(current->left) qu.push(current->left);
25                 if(current->right) qu.push(current->right);
26             }
27             level++;
28         }
29         return level;
30     }
31 };