如果根节点为空返回true
如果节点为空,并且左右节点都为空返回true,否则返回false
如果非空判断左子树的右节点和右子树的左节点是否相同,左子树的左节点和右子树的右节点是否相同
/**
* Definition for a binary tree node.
* struct TreeNode {
* int val;
* TreeNode *left;
* TreeNode *right;
* TreeNode(int x) : val(x), left(NULL), right(NULL) {}
* };
*/
class Solution {
public:
bool isSymmetric(TreeNode* root) {
return !root||dfs(root->left,root->right);
}
bool dfs(TreeNode *p,TreeNode *q)
{
if(!q||!p) return !p&&!q;
if(p->val!=q->val) return false;
return dfs(p->left,q->right) && dfs(q->left,p->right);
}
};