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.

/**
* 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) return 0;

int leftDepth = maxDepth(root->left);
int rightDepth = maxDepth(root->right);

if(leftDepth == 0 && rightDepth == 0) return 1;
if(leftDepth == 0) leftDepth = INT_MIN;
if(rightDepth == 0) rightDepth = INT_MIN;

return 1 + max(leftDepth, rightDepth);
}
};

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

Runtime: 8ms.

/**
* 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) return 0;

queue<TreeNode* > qu;
qu.push(root);
int level = 0;
while(!qu.empty()){
int n = qu.size();
while(n--){
TreeNode* current = qu.front();
qu.pop();

if(current->left) qu.push(current->left);
if(current->right) qu.push(current->right);
}
level++;
}
return level;
}
};