Challenge: Build a Transaction Validator in Rust

Apply your error handling knowledge using Rust's Result<T, E> type. You'll validate a transfer by checking multiple conditions and returning typed errors — the same pattern used in real Solana programs.

Your Task

Implement validate_transfer(sender, recipient, amount, sender_balance) that:

1. Returns Err("INVALID_RECIPIENT") if recipient is empty
2. Returns Err("ZERO_AMOUNT") if amount is 0
3. Returns Err("INSUFFICIENT_BALANCE") if sender_balance < amount
4. Returns Err("SAME_ACCOUNT") if sender equals recipient
5. Returns Ok(()) if all validations pass

Validation Order: Check in the order listed above (return the first error).

Rust Concepts Used:

• Result<(), String> return type
• Early returns with return Err(...)
• String comparison with ==
• The ? operator pattern (for learning)