leetcode 104. 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.

BFS或 DFS

/**
 * 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) //BFS
    {
        return maxD(root);
    }

    int maxD(TreeNode* root)
    {
        if (root == nullptr)
            return 0;

        return max(maxD(root->right)+1,maxD(root->left)+1);

    }*/

    int maxDepth(TreeNode* root) //DFS
    {
        queue<TreeNode*> q;
        int maxlen = 0;
        TreeNode* node = root;
        if(node==nullptr) return 0;
        q.push(node);

        while(!q.empty())
        {
           int size = q.size();
            while(size-- >0)
            {
                if(q.front()->left)
                    q.push(q.front()->left);
                 if(q.front()->right)
                    q.push(q.front()->right);
                q.pop();
            }
            maxlen++;
        }
        return maxlen;

    }


};