Flip Equivalent Binary Trees LeetCode solution in Java

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class Solution {
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  public boolean flipEquiv(TreeNode root1, TreeNode root2) {
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    return helper(root1, root2);
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  }
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  private boolean helper(TreeNode x, TreeNode y) {
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    if (x == null && y == null) return true;
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    if (x == null || y == null || x.val != y.val) return false;
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    boolean similarity =
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        helper(x.left, y.left) && helper(x.right, y.right); // check if 2 subtrees are similar
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    boolean swap =
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        helper(x.left, y.right)
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            && helper(
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                x.right,
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                y.left); // check if the 2 subtrees can be similar after swapping the left & right
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    // subtrees with each other
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    return similarity || swap; // if either true, means we can flip to match both trees
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  }
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}