leetcode-104-Maximum Depth of Binary Tree

                                                                                   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.

/** * 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 n=0;    int maxDepth(TreeNode* root) {  // 递归           if(root==NULL) return 0;  //为空则返回 0           return 1+max(maxDepth(root->left),maxDepth(root->right)); //不为空 则返回 左右子树的最大深度 加上1    }    int maxDepth(TreeNode* root) {  // 非递归        if(!root) return 0;        int num=0;   // 记录 最大深度        int count_=0;  // 每一层的节点数        queue<TreeNode*>q;        q.push(root);        count_=1;                while(!q.empty()){            TreeNode* x=q.front();            q.pop();            count_--;             if(x->left) q.push(x->left);            if(x->right) q.push(x->right);                        if(count_==0){ // count_==0 此层的节点访问完 num++                count_=q.size();                num++;            }        }        return num;    }};