9-liner using stack in reversed pre-order traversal

  • 0
        vector<int> postorderTraversal(TreeNode* r) {
            if (!r) return {};
            vector<int> rev;
            stack<TreeNode*> s; s.push(r);
            while (!s.empty()) {
                auto cur = s.top(); s.pop();
                if (cur->left) s.push(cur->left);
                if (cur->right) s.push(cur->right);
            return vector<int>(rev.rbegin(), rev.rend());

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