leetcode || 104、Maximum Depth of Binary Tree

problem：

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.

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题意：输出二叉树的深度

thinking：

深度优先搜索，记录最大深度

code：

/**
 * Definition for binary tree
 * 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==NULL)
            return 0;
        int max_dep=0;
        dfs(0,max_dep,root);
        return max_dep;
    }
protected:
    void dfs(int dep,int &max_dep,TreeNode *node)
    {
        if(node==NULL)
            return;
        dep++;
        max_dep = max(max_dep,dep);
        if(node->left!=NULL)
            dfs(dep,max_dep,node->left);
        if(node->right!=NULL)
            dfs(dep,max_dep,node->right);
    }
};