topic description
Please implement a function to judge whether a binary tree is symmetric. Note that a binary tree is defined as symmetric if it is identical to its mirror image.
/*
struct TreeNode {
int val;
struct TreeNode *left;
struct TreeNode *right;
TreeNode(int x) :
val(x), left(NULL), right(NULL) {
}
};
*/
class Solution {
public:
//把根节点的左右孩子当做两颗树，然后按相反的顺序遍历两颗树并对比
bool isSymmetrical(TreeNode* pRoot)
{
if (pRoot == nullptr)
return true;
return isSymmetrical(pRoot->left, pRoot->right);
}
private:
bool isSymmetrical(TreeNode* p1, TreeNode* p2)
{
if (p1 == nullptr && p2 == nullptr)
return true;
if (p1 == nullptr || p2 == nullptr)
return false;
if (p1->val != p2->val)
return false;
else
return isSymmetrical(p1->left, p2->right) && isSymmetrical(p2->left, p1->right);
}
};