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4. Find a Missing Number From a Sequence of Consecutive Numbers

Objective: write an algorithm to Find a Missing Number From a Sequence of Consecutive Numbers

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

Output: missing number

Approach:

  • The approach is very simple, Add all the given numbers say S
  • Calculate the 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 the sum of all the array elements which is = 48
So missing number will be = 55-48 = 7

 

Output:

Missing number is :6