18 树的子结构

输入两棵二叉树A，B，判断B是不是A的子结构。（ps：我们约定空树不是任意一个树的子结构）

C++:

/*
struct TreeNode {
    int val;
    struct TreeNode *left;
    struct TreeNode *right;
    TreeNode(int x) :
            val(x), left(NULL), right(NULL) {
    }
};*/
class Solution {
public:
    bool HasSubtree(TreeNode* pRoot1, TreeNode* pRoot2){
        bool result = false ;
        if (pRoot1 != NULL && pRoot2 != NULL){
            if (pRoot1->val == pRoot2->val)
                result = isSubtree(pRoot1 , pRoot2) ;
            if (!result)
                result = HasSubtree(pRoot1->left , pRoot2) ;
            if (!result)
                result = HasSubtree(pRoot1->right , pRoot2) ;
        }
        return result ;
    }
    
    bool isSubtree(TreeNode* pRoot1, TreeNode* pRoot2){
        if (pRoot2 == NULL)
            return true ;
        if (pRoot1 == NULL)
            return false ;
        if (pRoot1->val != pRoot2->val)
            return false ;
        return isSubtree(pRoot1->left , pRoot2->left) && isSubtree(pRoot1->right , pRoot2->right) ;
    }
};