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

/*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 maxDepth(TreeNode* root) {       //     }// };

#import 
    
     #import 
     
      typedef struct TreeNode TreeNode;struct TreeNode {    int val;    TreeNode *left;    TreeNode *right;    //    TreeNode(int x) : val(x), left(NULL), right(NULL) {}};TreeNode* MakeTreeNode(int x);void ConnectTreeNodes(TreeNode* pParent,TreeNode* pLeft,TreeNode* pRight);int maxDepth(TreeNode* root);int main (int argc, const char * argv[]){    @autoreleasepool {                // TEST        //            1        //         /      \        //        2        3        //       /\         \        //      4  5         6        //        /        //       7        //creat Nodes        TreeNode* pNode1 = MakeTreeNode(1);        TreeNode* pNode2 = MakeTreeNode(2);        TreeNode* pNode3 = MakeTreeNode(3);        TreeNode* pNode4 = MakeTreeNode(4);        TreeNode* pNode5 = MakeTreeNode(5);        TreeNode* pNode6 = MakeTreeNode(6);        TreeNode* pNode7 = MakeTreeNode(7);                //connect Nodes        ConnectTreeNodes(pNode1, pNode2, pNode3);        ConnectTreeNodes(pNode2, pNode4, pNode5);        ConnectTreeNodes(pNode3, NULL,   pNode6);        ConnectTreeNodes(pNode5, pNode7,  NULL );                int depth = maxDepth(pNode1);                NSLog(@"maxDepth is %d", depth);    }}TreeNode* MakeTreeNode(int x){    TreeNode *node = malloc(sizeof(TreeNode));    node->val   = x;    node->left  = NULL;    node->right = NULL;    return node;}void ConnectTreeNodes(TreeNode* pParent,TreeNode* pLeft,TreeNode* pRight){    if(pParent!=NULL)    {        pParent->left  = pLeft;        pParent->right = pRight;    }}int maxDepth(TreeNode* root) {    return root==NULL?0:1+MAX(maxDepth(root->left),maxDepth(root->right));}