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Created October 29, 2012 13:48
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Fibonacci sequence implemented in Prolog
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gistfile1.prolog
fib(0, 1) :- !.
fib(1, 1) :- !.
fib(N, Result) :- N1 is N - 1, N2 is N - 2, fib(N1, Result1), fib(N2, Result2), Result is Result1 + Result2.
@WodenWang820118
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WodenWang820118 commented May 21, 2021 •
edited
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fibonacci(0,1):-!. % cut down the backtracking
fibonacci(1,1):-!.

fibonacci(N,X):-
  N > 0, % the constraint to make N always greater than 0; put the integer less than 0 doesn't make sense
  N2 is N - 2, % it doesn't work to pass N-2 into the fibonacci predicate. The "is" is the arithmetic operation, not "=" in other languages 
  N1 is N - 1,
  fibonacci(N2,X2), % get the X2 value
  fibonacci(N1,X1), % get the X1 value
  X is X1 + X2. % calculate the Fibonacci number

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