Transcript Cs212: DataStructures

1
CS212: DATASTRUCTURES
Computer Science Department
Lab 3 : Recursion
Overview
2

Recursion is a function that calls itself

Repeats function (method) block of code until a specified condition is met
int factorial() {
... factorial() ...
}

When a recursive call is made, the function (method) clones itself, making new copies of

Code

Local variables

Parameters
21-Feb-14
Computer Science Department
Rules
3
1.
Every recursive function must have a base case.
2.
Every recursive function must make progress towards its
base case to prevent infinite recursion.

Anything that can be programmed using recursive functions
can be programmed without recursion.
21-Jul-15
Computer Science Department
Example1: Calculating Factorial
4


Factorial can be defined as follows

Factorial of 0 is 1

Factorial of N (for N>0) is N * N-1 * ... * 3 * 2 * 1
Iterative version of factorial
(JAVA)
(C++)
int factorial (int N)
{
int result = 1;
for (int i=1; i<= N; i++)
{ result = result * i;}
return result;
}
21-Jul-15
public static int factorial (int n)
{
int result = 1;
for (int i=1; i<= n; i++)
{ result = result * i;}
return result;
}
Computer Science Department
Calculating Factorial ( cont.)
5

Recursive version of factorial
Base case
(JAVA)
(C++)
Public static int factorial (int n)
{
if (N == 0)
return 1;
else
return N * factorial(N-1);
int factorial (int N)
{
if (N == 0)
return 1;
else
return N * factorial(N-1);
Recursive
calls
}
}
21-Jul-15
Computer Science Department
Example 2: Printing integers
6


Print integers from 1 to N.
Iterative version:
In C++
In Java
void printInt( int N )
{
for ( int i = 1 ; i<= N ; i++)
cout << i << endl ;
}
void printInt( int N )
{
for ( int i = 1 ; i<= N ; i++)
System.out.println(i) ;
}
21-Jul-15
Computer Science Department
Printing integers (cont.)
7

Recursive version:
In Java
In C++
void printInt( int N )
{
if (N == 0) return;
printInt( N - 1 );
cout << N << endl;
Base case
Public static void printInt(
int N )
{
if (N == 0) return;
printInt( N - 1 );
System.out.println( N );
Recursive
calls
}
}
21-Jul-15
Computer Science Department