# Write a Program to find duplicate number between 1 to N Numbers [Java interview]

###### Write a Program to find duplicate number between 1 to N Numbers

Here we have an array from 1 to N with one duplicate number.

e.g we have array from 1 to 10 and 2 is repeated once in this array. Then we need to find that 2 is a duplicate number in given array.

###### Java Program to find duplicate number between 1 to N Numbers ``````
package com.codenuclear;

public class FindDuplicateNumber {

public int findDuplicateNumber(int inputArray[],int N){

int sum = getSum(inputArray);

int dupNo = sum - (N*(N+1)/2);
return dupNo;
}

public int getSum(int numbers[]){

int sum = 0;
for(int num:numbers){
sum += num;
}
return sum;
}

public static void main(String args[]){

int N = 10;

// Below array is from 1 to 10 and 2 is repeated once.
int givenArray[] = {5,2,9,8,2,3,10,1,7,6,4};

FindDuplicateNumber obj = new FindDuplicateNumber ();

System.out.println("Duplicate Number is : "+obj.findDuplicateNumber(givenArray,N));
}
}
``````

Output Duplicate Number is : 2 