劍指offer：樹的子結構

題目描述：輸入兩顆二叉樹A，B，判斷B是不是A的子結構

/*
struct TreeNode {
    int val;
    struct TreeNode *left;
    struct TreeNode *right;
    TreeNode(int x) :
            val(x), left(NULL), right(NULL) {
    }
};*/
class Solution {
public:
    bool has(TreeNode * p1, TreeNode * p2)
        {
        if(!p2)
            return true;
        if(!p1)
            return false;
        if(p1->val != p2->val)
            return false;
        else
            return has(p1->left, p2->left) && has(p1->right, p2->right);
         
    }
    bool HasSubtree(TreeNode* pRoot1, TreeNode* pRoot2)
    {
        bool res=false;
        if(pRoot1 && pRoot2)
            {
            res = has(pRoot1, pRoot2);
            if(!res)
                {
                res = HasSubtree(pRoot1->left, pRoot2);
            }
            if(!res)
                {
                res =HasSubtree(pRoot1->right, pRoot2);
            }
        }
        return res;
    }
};