Invert Binary Tree LeetCode solution in Java

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class Solution {
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  public TreeNode invertTree(TreeNode root) {
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    swap(root);
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    return root;
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  }
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  private static void swap(TreeNode current) {
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    if (current == null) {
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      return;
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    }
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    swap(current.left);
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    swap(current.right);
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    TreeNode temp = current.left;
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    current.left = current.right;
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    current.right = temp;
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  }
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}