[LeetCode] 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

 

Note:
Bonus points if you could solve it both recursively and iteratively.

 

这题就是深搜，但是要同时搜两颗树，左子树和右子树。然后因为要是对称的，所以左子树要先搜左边，右子树要先搜右边，然后再反过来

这题说用迭代写出来可以bonus，暂时没写出来，不过也不会太难，这题迭代的深搜应该用两个栈吧，一个左栈一个右栈...(猜的

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

bool isSymmetric(TreeNode *root) {
    return symmetricIter(root->left, root->right);
}