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class Solution {
public:
    int depth;
    int maxDepth(TreeNode *root) {
        // Note: The Solution object is instantiated only once and is reused by each test case.
        if(root == NULL)
            return 0;
        depth = 1;
        query(root,1);
        return depth;
    }
    void query(TreeNode *node,int k)
    {
        if(node->left == NULL && node->right == NULL)
        {
            if(k > depth)
                depth = k;
        }
        if(node->left != NULL)
        {
            query(node->left,k+1);
        }
        if(node->right != NULL)
        {
            query(node->right,k+1);
        }
    }
};