Sum the root-to-leaf paths in a binary tree

SumRootToLeafPaths.java

/**
 * Problem: Design an algorithm to compute the sum of the binary numbers represented by the the
 * root-to-leaf path
 */
public class SumRootToLeafPaths {


    public int sumRootToLeaf(BinaryTreeNode<Integer> tree) {
        return sumRootToLeafHelper(tree, 0);
    }

    public int sumRootToLeafHelper(BinaryTreeNode<Integer> tree, int partialPathSum) {
        if (tree == null)
            return 0;
        partialPathSum = partialPathSum * 2 + tree.data;
        if (tree.left == null && tree.right == null) {
            return partialPathSum;
        }

        return sumRootToLeafHelper(tree.left, partialPathSum) +
                sumRootToLeafHelper(tree.right, partialPathSum);
    }
}