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.

我的解决方案：

/** * 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(NULL == root)            return 0;        int depth_l = maxDepth(root->left);        int depth_r = maxDepth(root->right);        return depth_l > depth_r  ? depth_l + 1:depth_r + 1;    }};

一行代码的解法：

int maxDepth(TreeNode *root){    return root == NULL ? 0 : max(maxDepth(root -> left), maxDepth(root -> right)) + 1;}

不用递归的解法：Breadth-first-search

int maxDepth(TreeNode *root){    if(root == NULL)        return 0;    int res = 0;    queue
     
       q;    q.push(root);    while(!q.empty())    {        ++ res;        for(int i = 0, n = q.size(); i < n; ++ i)        {            TreeNode *p = q.front();            q.pop();            if(p -> left != NULL)                q.push(p -> left);            if(p -> right != NULL)                q.push(p -> right);        }    }    return res;}
     

不用递归的解法2

int maxDepth(TreeNode *root){    if (root == NULL) return 0;    stack
     
       gray;    stack
      
        depth;    int out = 0;    gray.push(root);    depth.push(1);    while (!gray.empty()) {        TreeNode *tmp = gray.top();        int num = depth.top();        gray.pop();        depth.pop();        if (tmp->left == NULL && tmp->right == NULL) {            out = num > out ? num : out;        }        else {            if (tmp->left != NULL) {                gray.push(tmp->left);                depth.push(num + 1);            }            if (tmp->right != NULL) {                gray.push(tmp->right);                depth.push(num + 1);            }        }    }    return out;}
      
     

python 的解决方案：

# Definition for a  binary tree node# class TreeNode:#     def __init__(self, x):#         self.val = x#         self.left = None#         self.right = Noneclass Solution:    # @param root, a tree node    # @return an integer    def maxDepth(self, root):        def maxDepthHelper(root):            if not root: return 0            return max(1+maxDepthHelper(root.left), 1+maxDepthHelper(root.right))        return maxDepthHelper(root)