leetcode/Problems/0101.cpp at master · DimitrijeDobrota/leetcode · GitHub

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class Solution {
    string preorder(TreeNode *root, bool left) {
        if (!root) return "";

        string res;
        stack<TreeNode *> st;
        st.push(root);
        while (!st.empty()) {
            TreeNode *root = st.top();
            st.pop();
            if (!root) {
                res += "-";
                continue;
            }
            res += root->val;
            if (left) {
                st.push(root->right);
                st.push(root->left);
            } else {
                st.push(root->left);
                st.push(root->right);
            }
        }
        return res;
    }

  public:
    bool isSymmetric(TreeNode *root) {
        if (!root) return false;

        return preorder(root->left, true) == preorder(root->right, false);
    }
};