Implement a function to validate galactic transmission sequences. A sequence is valid if every opening signal is matched with a corresponding closing signal of the same frequency, and the signal pairs are properly nested.
Explanation: Step-by-step: with input S = 'AABBBG', we push 'A' onto the stack. Then we encounter 'B', which is a valid pair with 'A' on the stack. We push 'B' onto the stack. Then we encounter 'B' again, which is a valid pair with 'B' on the stack. Then we encounter 'B' again, which is a valid pair with 'B' on the stack. Then we encounter 'G', which does not have a corresponding opening signal, so the sequence is invalid.
Explanation: Step-by-step: with input S = 'AAABBB', we push 'A' onto the stack. Then we encounter 'A', which is a valid pair with 'A' on the stack. We push 'A' onto the stack. Then we encounter 'B', which is a valid pair with 'A' on the stack. We push 'B' onto the stack. Then we encounter 'B' again, which is a valid pair with 'B' on the stack. Then we encounter 'B' again, which is a valid pair with 'B' on the stack.
Master coding challenges related to Stack and solve the [Backup] Parsing Galactic Transmission Sequences problem optimally.
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