LeetCode 101. Symmetric Tree

Given a binary tree, check whether it is a mirror of itself (ie, symmetric around its center).

For example, this binary tree is symmetric:

1
/ \
2   2
/ \ / \
3  4 4  3

But the following is not:

1
/ \
2   2
\   \
3    3

static bool isSymmetric(TreeNode* left, TreeNode* right) {
if(!left && !right) return true;
if(!left && right) return false;
if(!right && left) return false;
return left->val == right->val && isSymmetric(left->left, right->right) && isSymmetric(left->right, right->left);
}
bool isSymmetric(TreeNode* root) {
if(!root) return true;
return isSymmetric(root->left, root->right);
}