[FEAT]: Implement a Merkle Tree

[beeguy74]

📝 [FEAT]: Implement a Merkle Tree

🛠️ Issue

• Closes [FEAT]: Implement a Merkle Tree #156

📖 Description

Implementation of a Merkle Tree contract. The contract handles the creation of Merkle trees and verification of data inclusion using Merkle proofs. I provided series of unit tests to ensure that all works fine.

build_tree returns the hashes of the nodes in the Merkle tree;
get_root returns the hash root of the tree;
verify requires Merkle proof array, hash root, hash of the value being verified and its index in the original data array
generate_merkle_proof requires the index of the target value and the length of initial data array

📝 Additional Notes

I refined the Merkle tree implementation from 'Starknet by Example': I added a support for odd input data arrays so provided tree is built as follows:

• The hashes of the transactions in the input data array are computed: hash(L1), hash(L2), hash(L3), and so on.
• Hashes of the sum of data hashes are then calculated, for example, hash(hash(L1) + hash(L2)). Since a Merkle tree is binary, the number of elements at each iteration must be even. Therefore, if the data array contains an odd number of elements, the last one is duplicated and combined with itself: hash(hash(L3) + hash(L3)).
• Next, the hashes of the sum of hashes are computed again. This process repeats until a single hash is obtained—the Merkle root.

[beeguy74]

@danielcdz I am ready for review, sir! 🦺

[danielcdz]

LGTM

[beeguy74]

Do you have some comments on this? should i change something?

[coxmars]

LGTM, thanks for your effort 🫡