This morning I passed by my secondary school campus. It has changed a lot with 2 brand new buildings. I started to learn programing in that school, where they taught me about palindrome and some very basic programming lessons. I don’t even remember what language was used back then. Probably basic.

Then I remember learning about OO and algorithms in university. One thing that still stick, well aside from some vague memory of OO principles, is recursive function. When I first heard about it, it’s a puzzle and very difficult to understand even when the source code is provided. But as I learned about it, I think it’s very clever.

It’s been 7-8 years since I wrote any code. I do shell scripts mostly which is just a bunch of procedures. Doesn’t require any algorithm. So I decided to write a recursive function which finds the smallest number from a list.

If I remember right, recursion involves 2 important parts. An ever reducing input data set and a finite condition. We feed the function a dataset, which returns a smaller dataset and in turn it’s fed to the same function. The result is returned to the previous level when a finite condition is met.

Here it is the source code. findMin is the recursive function. It compares the first number in a list with the rest of the numbers. When the rest of the numbers become just 1 number, a comparison result is returned. I certainly welcome any criticism or comments.

Yes I know I can do *Collections.min()* which probably is smarter and faster.

[code language=”java”]

import java.util.*;

public class Recurse {

public static void main(String args[]) {

// Create a list of random numbers

Random rand = new Random();

ArrayList<Integer> testData = new ArrayList<Integer>();

while ( testData.size() < 10 ) {

testData.add(rand.nextInt(99));

}

ArrayList<Integer> testDataCopy = new ArrayList<Integer>(testData);

// Display test data

System.out.println("Random numbers: " + testData.toString());

// Throw list into recursion

System.out.println("Smallest number: " + findMin(testData));

// Of course Java can do this for you

System.out.println("Result from Java Collections: " + Collections.min(testDataCopy));

}

public static int findMin(ArrayList<Integer> list) {

// If list is not 1 number, feed it back to same method

if (list.size() > 1) {

int tmpNum = list.get(0);

list.remove(0);

int tmpNum2 = findMin(list);

if (tmpNum < tmpNum2) {

return tmpNum;

} else {

return tmpNum2;

}

} else {

// Finite condition met, return number

return list.get(0);

}

}

}

[/code]

396 total views, 2 views today