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# Recursion

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### Recursion

1. 1. Recursion
2. 2. What is recursion• Looping without a loop statement• A function that is part of its own definition• Can only work if there’s a terminating condition, otherwise it goes forever (the base case)
3. 3. A recursive function• N Factorial• 1! = 1 2! = 1 x 2 = 2 3! = 1 x 2 x 3 = 2! x 3 = 6 N! = 1 x 2 x 3 x .... (N-2) x (N-1) x N = (N-1)! x N
4. 4. How recursion is handled• Every time a function is called, the function values, local variables, parameters and return addresses are pushed onto the stack.• Over and Over again• You might run out!
5. 5. Dry-running a recursive callProcedure Printsequence(n) n <- n-1 if n > 1 then Printsequence(n) endif output(n)EndProcedure
6. 6. Dry-running a recursive callProcedure Printsequence(n) n <- n-1 if n > 1 then output(n) Printsequence(n) endifEndProcedure
7. 7. How to write a recursive procedure• Code the general case Result = n * Factorial(n-1)• Code the base case Result = 1• Ensure that the base case is reached after a finite number of recursive calls