树的子结构

   bool DFS(TreeNode* pRoot1,TreeNode* pRoot2)
    {
        if(!pRoot2)
            return true;
        if(!pRoot1)
            return false;
        if(pRoot1->val != pRoot2->val)
            return false;
        return DFS(pRoot1->left , pRoot2->left) && DFS(pRoot1->right , pRoot2->right);
    }
    bool HasSubtree(TreeNode* pRoot1, TreeNode* pRoot2)
    {
        if(pRoot1 == NULL || pRoot2 == NULL)
            return false;
        return DFS(pRoot1,pRoot2)||
            HasSubtree(pRoot1->left,pRoot2)|| 
            HasSubtree(pRoot1->right,pRoot2);
    }