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Lecture22

# Lecture22 - ECS 30 Introduction to Programming and Problem...

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ECS 30 Introduction to Programming and Problem Solving François Gygi Department of Computer Science

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Lecture 22 Chapter 10 • Recursion Homework 6 due date moved to Sat Nov 19, 11:50pm
Recursion Some tasks can be decomposed into subtasks In some cases, a subtask looks just like the original task Example: compute the factorial of 5 5! = 5 * 4 * 3 * 2 * 1 5! = 5 * 4! A function that performs the subtask can be used to perform the original task

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Recursion The function implementing the factorial calculation is calling itself int fac (int n) { if ( n == 1 ) return 1; else return n * fac (n-1); }
Recursion Compare with the iterative implementation int fac(int n) { int i, product = 1; for ( i=2; i<=n; i++ ) product *= i; return product; }

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Defining a recursive function Identify the special case where the evaluation of the function is "simple" int fac(int n) { if ( n == 1 ) return 1; else return n * fac(n-1); }
Defining a recursive function Deal with the other cases, possibly including a recursive call int fac(int n) { if ( n == 1 ) return 1; else return n * fac(n-1); }

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