Jalebi Bai and Decks of Sweets

Jalebi Bai has two decks of sweets. These decks are represented by two strings `s` and `t` consisting of lowercase letters from the English alphabet. Each letter from 'a' to 'z' denotes a single type of sweet, e.g., ‘b’ denotes Barfi, 'r' denotes Rasgulla, etc. She wants to use these decks in her friend Laddu’s marriage. Instead of graciously accepting the gift, Laddu asks Jalebi Bai to first make