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class Solution {
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 public:
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  bool recur(TreeNode *root, int value) {
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    if (root == NULL) return true;
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    if (root->val != value) {
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      return false;
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    }
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    return recur(root->left, value) && recur(root->right, value);
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  }
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  bool isUnivalTree(TreeNode *root) {
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    if (root == NULL) return true;
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    int value = root->val;
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    return recur(root, value);
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  }
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};