title: Find Repetitive Element 1 N 1
signature: function find_repetitive_element_1_n_1(arr, n)
test_code: 
  
  -- SOLUTION CODE
  -- ============================================
  PLACEHOLDER_CODE_BODY
  
  -- TESTING CODE 
  -- ============================================
  function isCorrect(actual, expected)
      if type(expected) ~= type(actual) then
          return false
      end
      
      if type(expected) == 'table' then
          for k,v_expected in pairs(expected) do
              
              if actual[k] == nil then
                  return false
              end
              local v_actual = actual[k]
              if not isCorrect(v_actual, v_expected) then
                  return false
              end
              actual[k]=nil
          end
      
          if next(actual) then 
              return false
          end
          return true
      else
          return actual == expected
      end
  end
  
  function validateSolution(actual, expected)
      return isCorrect(actual,expected)
  end
  
  function driver(arr, n, expected)
      local exec_result;
      local status, error_msg = pcall(function () 
          exec_result=PLACEHOLDER_FN_NAME(arr, n) 
      end)
      if status then
          if validateSolution(exec_result,expected) then
              return "PASSED"
          end
          return "FAILED"
      else
          return string.format("ERROR=%s",string.gsub(error_msg,".*:[%d]+: ",""))
      end
  end
      
  function main()
      result = driver({4, 8, 27, 34, 39, 42, 43, 54, 72}, 5, 313)
      print(string.format("TEST-0...%s",result))
  
      result = driver({-38, -66, -38, -48, -96, 74, -32, -62, -34, -32, -88, -12, -8, -4}, 9, -520)
      print(string.format("TEST-1...%s",result))
  
      result = driver({0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 1, 1, 1, 1}, 8, -23)
      print(string.format("TEST-2...%s",result))
  
      result = driver({88, 86, 23, 81, 76, 16, 94, 64, 59, 50, 71, 62, 10, 89, 73, 64, 65, 96, 83, 40, 99, 40, 77, 33, 14, 62, 6, 89, 74, 96, 93, 29, 15, 93, 9, 58, 98, 76, 23, 23, 70, 99}, 31, 2101)
      print(string.format("TEST-3...%s",result))
  
      result = driver({-96, -94, -82, -64, -56, -40, -36, -34, -32, -24, -24, -22, -20, -20, -20, -18, -18, -12, -10, -6, 16, 20, 20, 22, 26, 30, 36, 46, 46, 50, 50, 52, 64, 64, 64, 68, 72, 74, 76, 92, 96, 98}, 28, 76)
      print(string.format("TEST-4...%s",result))
  
      result = driver({0, 1, 1, 1, 1, 0, 0, 0, 1, 1, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 1, 0, 0, 1, 1, 0, 1, 1}, 25, -288)
      print(string.format("TEST-5...%s",result))
  
      result = driver({2, 6, 7, 13, 19, 23, 37, 39, 42, 42, 43, 45, 52, 53, 55, 56, 59, 63, 66, 71, 76, 85, 86, 89, 92, 94, 96, 99}, 27, 1159)
      print(string.format("TEST-6...%s",result))
  
      result = driver({52, -56, -12, 78, 6, 32, 0, 36, 34, -54, -74, -32}, 11, -45)
      print(string.format("TEST-7...%s",result))
  
      result = driver({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}, 15, -86)
      print(string.format("TEST-8...%s",result))
  
      result = driver({10, 42, 50, 5, 74, 81, 30, 76, 6, 34, 86, 4, 77, 71, 96, 22, 34, 50, 35, 16, 60, 11, 21, 38}, 13, 951)
      print(string.format("TEST-9...%s",result))
  
  end
  
  main()
source_py: def find_repetitive_element_1_n_1(arr, n):
      return (sum(arr) - (((n - 1) * n) // 2))
source_cpp: int find_repetitive_element_1_n_1(vector<int> arr, int n) {
    return accumulate(arr.begin(), arr.end(), 0 ) - ( ( n - 1 ) * n / 2 );
  }