Binary Tree Inorder Traversal LeetCode solution in C++

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class Solution {
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 public:
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  vector<int> inorderTraversal(TreeNode *root) {
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    vector<int> nodes;
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    stack<TreeNode *> todo;
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    while (root || !todo.empty()) {
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      while (root) {
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        todo.push(root);
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        root = root->left;
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      }
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      root = todo.top();
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      todo.pop();
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      nodes.push_back(root->val);
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      root = root->right;
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    }
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    return nodes;
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  }
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};