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public class Codec {
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  // Encodes a tree to a single string.
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  public String serialize(TreeNode root) {
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    StringBuilder string = new StringBuilder();
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    traverse(root, string);
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    return string.toString();
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  }
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  private void traverse(TreeNode root, StringBuilder string) {
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    if (root == null) return;
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    string.append(root.val).append(",");
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    traverse(root.left, string);
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    traverse(root.right, string);
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  }
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  // Decodes your encoded data to tree.
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  public TreeNode deserialize(String data) {
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    if (data.isEmpty()) return null;
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    String[] dataArr = data.split(",");
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    TreeNode root = new TreeNode(Integer.parseInt(dataArr[0]));
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    for (int i = 1; i < dataArr.length; i++) insert(Integer.parseInt(dataArr[i]), root);
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    return root;
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  }
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  private void insert(int digit, TreeNode root) {
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    if (digit > root.val) {
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      if (root.right != null) insert(digit, root.right);
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      else root.right = new TreeNode(digit);
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    } else {
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      if (root.left != null) insert(digit, root.left);
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      else root.left = new TreeNode(digit);
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    }
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  }
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}