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Language/Type: PHP recursion

Write a recursive function named hash_string that accepts an integer parameter $k and returns a String of # (hash symbols) that is 2k characters long (i.e., 2 to the $kth power). For example, the call of hash_string(3) returns "########".

If passed a value for $k less than 0, your function should throw an Exception with the message, "Error: argument must be non-negative."


  • Do not use any loops; you must use recursion.
Function: Write a PHP function as described, not a complete program.

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