7. Find missing and Repeating elements

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7. Find missing and Repeating elements


Problem link :- click here


package program;

public class Searching__7
{

	/*
	 	Given an unsorted array arr[] of size n of positive integers. One number 
	 	'A' from set{1, 2, 3, 4, 5, ....... n} is missing and one number 'B' occurs
	 	twice in array. Find these two numbers
	 	
	  	We have solved a similar question in array where we are asked to find the 
        duplicate elements in the array which contains only elements from 0 to n-1
	  	
	  	here the only difference is elements are from 0 to n
	 */
	
	static int[] findTwoElements(int arr[], int n)
	{
		int ans[] = new int[2];
		
		//first check which element is repeating
		for(int i=0; i<n; i++)
		{
			if( arr[ Math.abs(arr[i]) - 1 ]    >   0 )
				arr[ Math.abs(arr[i]) - 1 ] =  -arr[ Math.abs(arr[i]) - 1 ];
			else
			{
				ans[1] = Math.abs( arr[i] );
				break;              //because only one element is repeated
			}
		}
		
		for(int i=0; i<n; i++)
		{
			if(arr[i] > 0)
			{
				ans[0] = i + 1;
				break;
			}
		}
		
		return ans;
	}
	
	public static void main(String[] args)
	{
		int arr[] = {1, 3, 3};
		int ans[] = findTwoElements(arr, arr.length);
		
		System.out.println("Missing and Repeating elements are : ");
		for(int i=0; i<ans.length; i++)
			System.out.print(ans[i] + " ");
	}

}

Time complexity :- O(n)
Space complexity :- O(1)

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