typedef struct TNode {
   int m_Data;
   struct TNode * m_L, * m_R;
} TNODE;

int maxDepth (TNODE * root) {
    if (!root)return 0;
    int left = maxDepth(root->m_L);
    int right = maxDepth(root->m_R);
    return 1+(left > right ? left : right);
}