Thread: Help with Java coding problem!

This is a problem I have been struggling with, think I'm almost there with it just need a nudge in the right direction. I'm not looking for the answer, just some 'hints'

The Problem
////////////////////////////// PROBLEM STATEMENT //////////////////////////////
// Given an array of ints of any length, print an array with the elements //
// "rotated left" by the specified amount. Use methods for array input, //
// rotating the array and printing the array. //
// {1, 2, 3} 1 -> {2, 3, 1} //
// {5, 11, 9} 2 -> {9, 5, 11} //
// {7, 0, 0} 3 -> {7, 0, 0} //
///////////////////////////////////////////////////////////////////////////////

I have all my methods set up, just not sure how to write the code for the rotateArray(); method.

So far I've tried swapping each element in the array within a decreasing for loop, but I having trouble with the front element that has to be carried to the end of the array.

(In the problem statement - {1, 2, 3} is the actual given array and the number following is how many times it must be 'rotated left'. Then the second set of curly braces is the expected result.

Wow, great advice. The physical deck of cards made me visualize the problem a lot better.

This is how I plan to solve this problem.

I will create a loop that calls the rotateLeft(); method 'n' amount of times.

Within the rotateLeft() method I will store element 0 into a temp variable then swap each element going up the array until I reach array.length - 1, where I will place the int stored in my temp variable.

Does that sound about right?

Originally Posted by KevinWorkman

How would you do this by hand, with a piece of paper and a pencil instead of a computer? Pretend you are given a deck of cards, and you're supposed to implement this algorithm on it. How do you do it?

import java.util.*; public class H1D4 {public static void main (String[] args) {while (JPL.test()) {

////////////////////////////// PROBLEM STATEMENT //////////////////////////////
// Given an array of ints of any length, print an array with the elements //
// "rotated left" by the specified amount. Use methods for array input, //
// rotating the array and printing the array. //
// {1, 2, 3} 1 -> {2, 3, 1} //
// {5, 11, 9} 2 -> {9, 5, 11} //
// {7, 0, 0} 3 -> {7, 0, 0} //
///////////////////////////////////////////////////////////////////////////////

// >>>>>> Your Java Code Fragment starts here <<<<<<
Scanner keyboard = new Scanner(System.in);
int[] mainArray = getArray(keyboard);
int[] result = rotateArray(mainArray, keyboard);
printArray(result);
// >>>>>> Your Java Code Fragment ends here <<<<<<
}}

// >>>>>> Your Java Methods start here <<<<<<
static int[] getArray(Scanner kb)
{
int n = kb.nextInt();
int[] a = new int[n];
for (int i = 0; i < a.length; i++)
a[i] = kb.nextInt();
return a;
}

static int[] rotateArray(int[] a, Scanner kb)
{
int n = kb.nextInt();
for (int k = n; k > 0; k--)
{
int lastChar = a[0];
for (int i = 0; i < a.length -1 ; i++)
{
a[i] = a[i+1];
}
a[a.length - 1] = lastChar;
}
return a;
}

static void printArray(int[] a)
{
for (int i = 0; i < a.length; i++)
System.out.print(a[i]);
}




// >>>>>> Your Java Methods end here <<<<<<
}


Thank you very much for your help, this algorithm solved the problem. Simple after I had visualized it with the deck of cards, what great advice!