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class Solution {
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 public:
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  TreeNode *trimBST(TreeNode *root, int low, int high) {
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    if (!root) return NULL;
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    root->left = trimBST(root->left, low, high);
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    root->right = trimBST(root->right, low, high);
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    if (root->val < low) {
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      if (root->right) {
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        TreeNode *temp = root;
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        // delete root;
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        return temp->right;
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      } else {
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        return NULL;
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      }
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    }
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    if (root->val > high) {
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      if (root->left) {
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        TreeNode *temp = root;
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        // delete root;
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        return temp->left;
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      } else {
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        return NULL;
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      }
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    }
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    return root;
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  }
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};