Find out duplicate number between 1 to N numbers.

package com.java2novice.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));

}