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class Solution {
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  public int sumRootToLeaf(TreeNode root) {
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    return sumRootToLeaf(root, 0);
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  }
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  public int sumRootToLeaf(TreeNode root, int sum) {
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    if (root == null) return 0;
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    sum = (2 * sum) + root.val;
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    if (root.left == null && root.right == null) return sum;
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    return sumRootToLeaf(root.left, sum) + sumRootToLeaf(root.right, sum);
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  }
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}