General Algorithms

1. Given an array of n numbers having elements from 1 to n with one number missing. Find the missing number                                                                                                                    Algorithm 1

   1. Get the sum of numbers 
          total = n*(n+1)/2
   2  Subtract all the numbers from sum and
      you will get the missing number.

   Algorithm 2 

   1) XOR all the array elements, let the result of XOR be X1.
   2) XOR all numbers from 1 to n, let XOR be X2.
   3) XOR of X1 and X2 gives the missing number. 

2. Euclid’s Algorithm                                                            int GCD(int A, int B) { if(B==0) return A;                                                           else return GCD(B, A % B); }