Question 1

Another method for compressing data is Huffman coding. In Huffman coding, the codes for the characters can be created based on their position in a tree.
**Figure 3** shows a Huffman code for each different character in the string in **Figure 2**.
Complete the Huffman tree below to show the position of the characters I, S and P using the codes from **Figure 3**.

Accepted Answer

1.  **Understand Huffman Trees:** In a Huffman tree, moving down a left branch represents a `0` and moving down a right branch represents a `1`. The code for a character is the sequence of 0s and 1s you follow from the root (top) node to reach that character's leaf node.
2.  **Trace the codes:**
    *   **I (code 0):** Starting from the root (11), the code `0` means we take the left branch. This leads directly to the first empty box. So, **I** goes in the box connected to the root node on the left.
    *   **S (code 11):** Starting from the root (11), `1` means take the right branch to node (7). The next `1` means take the right branch from node (7). This leads to the empty box on the far right. So, **S** goes in the box connected to node 7 on the right.
    *   **P (code 101):** Starting from the root (11), `1` means right branch to node (7). `0` means left branch to node (3). `1` means right branch from node (3). This leads to the empty box next to M. So, **P** goes in the box connected to node 3 on the right.
3.  **Check M (code 100):** Root(11) -> right(1) to node(7) -> left(0) to node(3) -> left(0) to M. This matches the diagram.

Question 2

What mistakes do candidates make on this AQA GCSE question?

Accepted Answer

✗ Placing characters in the wrong boxes.
✗ Confusing the left (0) and right (1) branches.
✗ Not starting from the root node for each character.

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