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.
For example:
Given binary tree [3,9,20,null,null,15,7],
3
/
9 20
/
15 7
return its depth = 3.
1 int maxDepth(TreeNode* root) { 2 if (!root) 3 return 0; 4 int left=maxDepth(root->left); 5 int right=maxDepth(root->right); 6 return left>=right?left+1:right+1; 7 }