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Language/Type: PHP recursion string return

Write a recursive function named digits_sorted that takes an integer as a parameter and returns true if the digits of the integer are sorted and false otherwise. The digits must be sorted in non-decreasing order when from left to right.

An integer that consists of a single digit is sorted by definition. The function should be also able to handle negative numbers. Negative numbers are also considered sorted if their digits are in non-decreasing order.

The following table shows several calls to your function and their expected return values:

Call Value Returned
digits_sorted(0) true
digits_sorted(2345) true
digits_sorted(-2345) true
digits_sorted(22334455) true
digits_sorted(-5) true
digits_sorted(4321) false
digits_sorted(24378) false
digits_sorted(21) false
digits_sorted(-33331) false


  • Do not declare any global variables.
  • Do not use any loops; you must use recursion.
  • Do not use any auxiliary data structures (e.g. arrays) or strings to solve this problem.
  • You can declare as many primitive variables (e.g. integers) as you like.
  • You are allowed to define other "helper" functions if you like; they are subject to these same constraints.
Function: Write a PHP function as described, not a complete program.

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