Given a binary tree, check whether it is a mirror of itself (ie, symmetric around its center).
For example, this binary tree [1,2,2,3,4,4,3]
is symmetric:
1
/ \
2 2
/ \ / \
3 4 4 3
But the following [1,2,2,null,3,null,3]
is not:
1
/ \
2 2
\ \
3 3
判断一个树是不是镜像对称的。跟判断两棵树是不是相同的区别在于,SameTree判断两棵树左右子树是否相等,判断对称树则是判断树的左子树是否和右子树相等,右子树是否跟左子树相等。
/**
* 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:
vector<int> tem;
void helper(TreeNode* root){
if(root==NULL) return;
helper(root->left);
tem.push_back(root->val);
helper(root->right);
}
bool isSymmetric(TreeNode* root) {
if(root==NULL) return true;
if(root->left==NULL && root->right==NULL) return true;
helper(root);
for(int i=0,j=tem.size()-1; i<=j;i++,j--){
if(tem[i]!=tem[j]) return false;
}
return true;
}
};