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Sum of natural numbers 1..n using recursion

This illustrates how to sum natural numbers using tail recursion. In some languages, tail call optimization is performed, which enables recursive calls to take constant stack space.

Code
Diff
  • def sum n
    def acc(n, s)
        return s if n <= 0 # Base case
        acc(n - 1, s + n)  # Recursion step, with accumulator
    end
    acc(n, 0)
end
    • def sum n
    • return 1 if n == 1 # Base case of recursion method - must be defined; otherwise infinite recursion may occur
    • n + sum(n - 1)
    • def acc(n, s)
    • return s if n <= 0 # Base case
    • acc(n - 1, s + n) # Recursion step, with accumulator
    • end
    • acc(n, 0)
    • end