title: Find The Missing Number 2
signature: class Solution {
  
      public Integer findTheMissingNumber2(ArrayList<Integer> a, Integer n) {
test_code: import static java.util.Map.entry;  
  import java.util.*;
  import java.lang.*;
  // TESTING CODE 
  // ============================================
  class QuestionEvaluator {
      public static String validateSolution(ArrayList<Integer> a, Integer n, Integer expected){
          try{
              Driver driver = new Driver();
              if (driver.run(a, n,expected)){
                  return "PASSED";
              }
              return "FAILED";
              
          } catch (Exception exception_obj){
              return exception_obj.getClass().getSimpleName();
          }
  
      }
      public static void main(String[] args) {
          String result;
          result = validateSolution(new ArrayList<>(Arrays.asList(2, 5, 7, 8, 10, 14, 27, 32, 51, 52, 57, 58, 65, 68, 68, 72, 73, 73, 83, 92, 98)), 12, 50);
          System.out.println(String.format("%s%s","TEST-0...",result));    
      
          result = validateSolution(new ArrayList<>(Arrays.asList(-60, -48, 38, -78, 88, 86, -4, -94, 16, -64, 32, 88, 58, -78, -16, 48, 38, 30, 66, -60, 20, 40, -28, -64, -48, -86, -80, -8, -58, 52, 80, -32, 46, -4, -70, 76, -4, 78, -64, 38, -40)), 28, -91);
          System.out.println(String.format("%s%s","TEST-1...",result));    
      
          result = validateSolution(new ArrayList<>(Arrays.asList(0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1)), 38, 1);
          System.out.println(String.format("%s%s","TEST-2...",result));    
      
          result = validateSolution(new ArrayList<>(Arrays.asList(69, 59, 22, 33, 69, 28, 11, 34, 72, 88, 16, 30, 69, 89, 43, 4, 65, 85, 27)), 13, 109);
          System.out.println(String.format("%s%s","TEST-3...",result));    
      
          result = validateSolution(new ArrayList<>(Arrays.asList(-98, -98, -92, -88, -88, -82, -74, -70, -68, -60, -60, -48, -38, -34, -34, -24, 14, 38, 50, 58, 62, 64, 64, 68, 76, 78, 78, 86, 88, 90, 92, 98, 98)), 23, 94);
          System.out.println(String.format("%s%s","TEST-4...",result));    
      
          result = validateSolution(new ArrayList<>(Arrays.asList(0, 1, 0, 1, 0, 1, 1, 0, 0, 1, 1, 0, 0, 1, 1, 0, 0, 1, 1, 1, 0, 1, 0, 0, 0, 0, 1, 1, 0, 0, 0, 1, 1, 1, 1, 1, 0, 1, 1, 1, 1, 0, 1, 1, 1, 1, 0, 0)), 41, 42);
          System.out.println(String.format("%s%s","TEST-5...",result));    
      
          result = validateSolution(new ArrayList<>(Arrays.asList(1, 9, 12, 12, 24, 25, 33, 33, 36, 39, 46, 48, 48, 52, 52, 53, 57, 69, 71, 72, 75, 76, 78, 80, 82, 86, 89, 91, 94, 95, 96, 97, 98, 99)), 30, 124);
          System.out.println(String.format("%s%s","TEST-6...",result));    
      
          result = validateSolution(new ArrayList<>(Arrays.asList(62, -66, 60, -92, 46, 6, -52, 48, 72, -64, 34, 20, 50, 70, -34, 20, -70, 14, -44, 66, -70)), 17, 101);
          System.out.println(String.format("%s%s","TEST-7...",result));    
      
          result = validateSolution(new ArrayList<>(Arrays.asList(0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1)), 30, 0);
          System.out.println(String.format("%s%s","TEST-8...",result));    
      
          result = validateSolution(new ArrayList<>(Arrays.asList(33, 10, 6, 71, 18, 22, 15, 57, 56, 63, 35, 93, 31, 43, 98, 99, 62, 39, 44, 86, 78, 95, 6, 76, 71)), 12, 32);
          System.out.println(String.format("%s%s","TEST-9...",result));    
      
      }
  }
  
  class Driver{
      public boolean run(ArrayList<Integer> a, Integer n, Integer expected){
  
          PLACEHOLDER_CLS_NAME sol = new PLACEHOLDER_CLS_NAME();
          return validateSolution(sol.PLACEHOLDER_FN_NAME(a, n),expected);
      }
      
      public boolean validateSolution(Integer actual, Integer expected){
          return actual.equals(expected);
      }
  }
  
  
  // SOLUTION CODE
  // ============================================
  PLACEHOLDER_CODE_BODY
source_py: def find_the_missing_number_2(a, n):
      x1 = a[0]
      x2 = 1
      for i in range(1, n):
          x1 = (x1 ^ a[i])
      for i in range(2, (n + 2)):
          x2 = (x2 ^ i)
      return (x1 ^ x2)
source_cpp: int find_the_missing_number_2(vector<int> a, int n) {
    int x1 = a [ 0 ];
    int x2 = 1;
    for ( int i = 1;
    i < n;
    i ++ ) x1 = x1 ^ a [ i ];
    for ( int i = 2;
    i <= n + 1;
    i ++ ) x2 = x2 ^ i;
    return ( x1 ^ x2 );
  }