Find out duplicate number between 1 to N numbers.

Description:

You have got a range of numbers between 1 to N, where one of the number is repeated. You need to write a program to find out the duplicate number.

Code:

? 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 package com.govindsblog.algos;   import java.util.ArrayList; import java.util.List;   public class DuplicateNumber {       public int findDuplicateNumber(List<Integer> numbers){                   int highestNumber = numbers.size() - 1;         int total = getSum(numbers);         int duplicate = total - (highestNumber*(highestNumber+1)/2);         return duplicate;     }           public int getSum(List<Integer> numbers){                   int sum = 0;         for(int num:numbers){             sum += num;         }         return sum;     }           public static void main(String a[]){         List<Integer> numbers = new ArrayList<Integer>();         for(int i=1;i<30;i++){             numbers.add(i);         }         //add duplicate number into the list         numbers.add(22);         DuplicateNumber dn = new DuplicateNumber();         System.out.println("Duplicate Number: "+dn.findDuplicateNumber(numbers));     } }

Output:

Duplicate Number: 22