1. class Solution {
  2.     // approach: sum of n-natural numbers
  3.     public int missingNumber(int[] nums) {
  4.         int n = nums.length;
  5.         int sum1 = (n*(n+1))/2;
  6.  
  7.         int sum2 = 0;
  8.         for(int ele : nums)
  9.             sum2 += ele;
  10.  
  11.         return sum1 - sum2;
  12.     }
  13.     // approach: XOR (a^a = 0)
  14.     public int missingNumber(int[] nums) {
  15.         int n = nums.length;
  16.         int xor1 = 0;
  17.         for(int i=1; i<=n; i++)
  18.         {
  19.             xor1 = xor1 ^ i;
  20.         }
  21.         int xor2 = 0;
  22.         for(int ele : nums)
  23.         {
  24.             xor2 = xor2 ^ ele;
  25.         }
  26.         return xor1 ^ xor2;
  27.     }
  28. }