Draw the recursion trace for the execution of the method PuzzleSolve(3, S, U) (Code Fragment 5.11), where S is empty and U = {a,b,c,d}. (Page 221 of the book mentioned below - R-5.6) Here is code Fragment 5.11 (page 213) from Goodrich, Michael T., Roberto Tamassia, Michael Goldwasser. Data Structures and Algorithms in Java, 6th Edition Algorithm PuzzleSolve(k, S, U): Input: An integer k, sequence S, and set U Output: An enumeration of all k-length extensions to S using elements in U without repetitions for each e in U do Add e to the end of S Remove e from U if k == 1 then Test whether S is a configuration that solves the puzzle if S solves the puzzle then add S to output else PuzzleSolve(k ? 1, S, U ) Remove e from the end of S Add e back to U

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