判斷一個二叉樹是不是另一個二叉樹的子結構

輸入兩棵二叉樹A，B，判斷B是不是A的子結構。約定空樹不是任意一個樹的子結構

class Solution {
    bool isSubtree(TreeNode* pRootA, TreeNode* pRootB) {
        if (pRootB == NULL) return true;
        if (pRootA == NULL) return false;
        if (pRootB->val == pRootA->val) {
            return isSubtree(pRootA->left, pRootB->left)&& isSubtree(pRootA->right, pRootB->right);
        } 
        else 
            return false;
    }

    public:
        bool HasSubtree(TreeNode* pRootA, TreeNode* pRootB)    {
            if (pRootA == NULL || pRootB == NULL) return false;
            return isSubtree(pRootA, pRootB) || HasSubtree(pRootA->left, pRootB) || HasSubtree(pRootA->right, pRootB);
        }
};