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.

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/**
* 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 preOrder(TreeNode *root, int hight, int &maxH) {

if(root!=NULL) {
if(hight>maxH) maxH=hight;
preOrder(root->left, hight+1, maxH);
preOrder(root->right, hight+1, maxH);
}

return maxH;
}
int maxDepth(TreeNode* root) {
int maxH = 0;
if(root==NULL) return 0;
return preOrder(root, 1, maxH);
}
};