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class Solution {
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  public boolean isSymmetric(TreeNode root) {
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    return isSymmetric(root.left, root.right);
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  }
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  public boolean isSymmetric(TreeNode rootLeft, TreeNode rootRight) {
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    if (rootLeft == null && rootRight == null) {
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      return true;
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    }
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    if (rootLeft == null || rootRight == null) {
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      return false;
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    }
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    if (rootLeft.val != rootRight.val) {
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      return false;
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    } else
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      return isSymmetric(rootLeft.right, rootRight.left)
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          && isSymmetric(rootLeft.left, rootRight.right);
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  }
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}