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 04032013, 05:41 AM #1Senior Member
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Didn't understand how Index value is returned.
Please consider the following program:
Java Code:import java.io.*; public class RotatedArrayAgain { public static void main(String[] args) throws IOException { int[] array = {12,13,15,16,21,3,4,5,6}; int len = array.length; System.out.println("Enter the Number to be searched"); InputStreamReader in = new InputStreamReader(System.in); BufferedReader bf = new BufferedReader(in); int target = Integer.parseInt(bf.readLine()); System.out.println("The Number Entered by the user is : " + target + "\n Let's see if it's there in the Rotated Array or Not :)"); int index = RotatedArray(array,len,target); if(index == 1){ System.out.println("The Number is not in the ARRAY ! Sorry !"); } else { System.out.println("The number is found at the index" + index); } } public static int RotatedArray(int a[], int n , int target){ int low = 0,high = a.length1; while (low <= high){ int mid = (low + high)/2; //CASE 1: If target is the middle element if( target == a[mid]){ return mid; } // CASE 2: If the Element is in Right Sorted Array else if (a[mid] <= a[high]){ if ( target > a[mid] && target < a[high]) low = mid + 1; else high = mid  1; } // CASE 3: If the Element is in Left Sorted Array else if ( a[low] <= a[mid]){ if (target > a[low] && target < a[mid]){ high = mid1; //low = mid + 1; }else low = mid+1; } }// END WHILE return 1; } }
Java Code:Enter the Number to be searched 15 The Number Entered by the user is : 15 Let's see if it's there in the Rotated Array or Not :) The number is found at the index 2
I didn't understand how the index of the array is getting printed properly in the above problem. My concern is with the following part of the code snippet from the above program:
Java Code:if(index == 1){ System.out.println("The Number is not in the ARRAY ! Sorry !"); } else { System.out.println("The number is found at the index" + index); }
Please help !
Thanks in advance.
 04032013, 06:05 AM #2Senior Member
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Re: Didn't understand how Index value is returned.
I think your RotatedArray method trying to find the index of the target element by dividing the array into two part. The left sorted part and the right sorted part. So it can quickly find the target element. When the target is smaller that the middle element it search to the left. When it bigger it search to the right. It will repeat until the target element found. If not it return 1.
Website: Learn Java by Examples
 04032013, 08:19 AM #3Senior Member
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 04032013, 08:21 AM #4Senior Member
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 04032013, 10:43 AM #5Senior Member
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Re: Didn't understand how Index value is returned.
I understand that "int index = RotatedArray(array,len,target);", that is index is getting some value from the method RotatedArray but if we consider Case 2 and 3, I haven't specified any return statement just like in Case 1 where I'm returning mid explicitly. This is what I'm not understanding. Please clarify.
 04032013, 11:19 AM #6Senior Member
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Re: Didn't understand how Index value is returned.
I suggest that you try to simulate the code using pencil and paper. Write down the value of every variable you have there for each steps in the loop. In a quick look what I can see that the case 2 and case 3 modify the value of low and high. Which will give a changing the value of mid variable in the next loop. And at some point this will make the case 1 become true (target == a[mid]) and return mid as the found index. Otherwise you method will return 1.
So get a pencil and paper and trace your code.Website: Learn Java by Examples
 04032013, 12:45 PM #7Senior Member
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