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class Solution {
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 public:
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  bool mirror(TreeNode *root1, TreeNode *root2) {
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    if (root1 == NULL and root2 == NULL) return true;
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    if (root1 == NULL or root2 == NULL) return false;
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    if (root1->val != root2->val) return false;
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    return mirror(root1->left, root2->right) and mirror(root1->right, root2->left);
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  }
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  bool isSymmetric(TreeNode *root) {
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    if (root == NULL) return true;
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    return mirror(root->left, root->right);
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  }
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};