# Find a Missing Number From a Sequence of Consecutive Numbers

Objective : You have been asked to Write an algorithm Find a Missing Number From a Sequence of Consecutive Numbers

Input:  Array, arrA[] with a missing number and Range

Output : missing number

Approach:

• Approach is very simple, Add all the given numbers say S
• Calculate sum of N numbers by formula n(n+1)/2 , say N
• Find missing number m = N-S

Example : suppose array given is  {1,2,3,4,5,6,8,9,10} and range is 10.

So N will be sum of 1 to 10  = 10(10+1)/2 = 55

S will be sum of all the array elements which is = 48

So missing number will be = 55-48 = 7

Complete Code:

 //find the missing number from the sequence of consecutive number //Approach is very simple, Add all the given numbers say S //Calculate sum of N numbers by formula n(n+1)/2 , say N //Find missing number m = N-S public class FindMissingNumber { int Sum; int Sum_N; public int missingNumber(int [] arrA, int size){ Sum_N = size*(size+1)/2; for(int i=0;i

Output :
Missing number is :6