title: Find The Element That Appears Once
signature: function findTheElementThatAppearsOnce(arr: Array<number>, n: number): number {
source_py: def find_the_element_that_appears_once(arr, n):
      ones = 0
      twos = 0
      for i in range(n):
          twos = (twos | (ones & arr[i]))
          ones = (ones ^ arr[i])
          common_bit_mask = (~ (ones & twos))
          ones &= common_bit_mask
          twos &= common_bit_mask
      return ones
source_cpp: int find_the_element_that_appears_once(vector<int> arr, int n) {
    int ones = 0, twos = 0;
    int common_bit_mask;
    for ( int i = 0;
    i < n;
    i ++ ) {
      twos = twos | ( ones & arr [ i ] );
      ones = ones ^ arr [ i ];
      common_bit_mask = ~ ( ones & twos );
      ones &= common_bit_mask;
      twos &= common_bit_mask;
    }
    return ones;
  }
question_info.test_list: [{"idx": 0, "outputs": 72, "inputs": {"arr": [7, 26, 26, 48, 59, 62, 66, 70, 72, 75, 76, 81, 97, 98], "n": 7}}, {"idx": 1, "outputs": -28, "inputs": {"arr": [-42, -48, -64, -74, 56, -34, 20, 16, 34, -84, 86, 38, 56, -86, 30, -74, -96, 96, 12, 10, -46, 10, -36, 38, 34, -46, -20, 14, 12, 62, -54, 20, -82, 24, 96], "n": 27}}, {"idx": 2, "outputs": 1, "inputs": {"arr": [0, 0, 1, 1], "n": 3}}, {"idx": 3, "outputs": 25, "inputs": {"arr": [68, 91, 61, 6, 32, 47, 76, 69, 44, 71, 29, 79, 74, 33, 44, 33, 45, 75, 43, 82, 83, 81, 95, 16, 86, 33, 69, 61, 73, 21, 54, 17, 98, 62, 14, 72, 80, 31, 56, 82, 14, 48, 76], "n": 38}}, {"idx": 4, "outputs": 104, "inputs": {"arr": [-98, -96, -92, -62, -52, -42, -42, -26, 4, 10, 14, 38, 64, 66, 72, 74, 82], "n": 14}}, {"idx": 5, "outputs": 0, "inputs": {"arr": [0, 1, 1, 1, 0, 0, 0, 1, 0, 1], "n": 5}}, {"idx": 6, "outputs": 10, "inputs": {"arr": [53, 63, 63], "n": 2}}, {"idx": 7, "outputs": 34, "inputs": {"arr": [-96, -38, -26, -46, 68, -36, 20, -18, -10, 52, 40, 94, -8, -64, 82, -22], "n": 15}}, {"idx": 8, "outputs": 0, "inputs": {"arr": [0, 0, 0, 0, 0, 1, 1], "n": 3}}, {"idx": 9, "outputs": 1, "inputs": {"arr": [99, 46, 48, 81, 27, 97, 26, 50, 77, 32, 45, 99, 46], "n": 12}}]
question_info.entry_cls_name: Solution
question_info.test_code: 
  
  // SOLUTION CODE
  // ============================================
  PLACEHOLDER_CODE_BODY
  
  // TESTING CODE 
  // ============================================
  function convertToString(value: any): string{
      return JSON.stringify(value, function (key, val) {
          if (val instanceof Set) {
              return Array.from(val);
          } return val;});
  }
  
  function validateSolution(actual: number, expected: number): boolean {
      return convertToString(actual) === convertToString(expected);
  }
  
  function driver(arr: Array<number>, n: number, expected:number): string {
      try{
          if (validateSolution(PLACEHOLDER_FN_NAME(arr, n),expected)){
              return "PASSED";
          }
          return "FAILED";
      } catch (error) {
        return error.name;
      }
      
  }
      
  function main(){
    let result = '';
    result = driver([7, 26, 26, 48, 59, 62, 66, 70, 72, 75, 76, 81, 97, 98], 7, 72);
    console.log(`TEST-0...${result}`);
  
    result = driver([-42, -48, -64, -74, 56, -34, 20, 16, 34, -84, 86, 38, 56, -86, 30, -74, -96, 96, 12, 10, -46, 10, -36, 38, 34, -46, -20, 14, 12, 62, -54, 20, -82, 24, 96], 27, -28);
    console.log(`TEST-1...${result}`);
  
    result = driver([0, 0, 1, 1], 3, 1);
    console.log(`TEST-2...${result}`);
  
    result = driver([68, 91, 61, 6, 32, 47, 76, 69, 44, 71, 29, 79, 74, 33, 44, 33, 45, 75, 43, 82, 83, 81, 95, 16, 86, 33, 69, 61, 73, 21, 54, 17, 98, 62, 14, 72, 80, 31, 56, 82, 14, 48, 76], 38, 25);
    console.log(`TEST-3...${result}`);
  
    result = driver([-98, -96, -92, -62, -52, -42, -42, -26, 4, 10, 14, 38, 64, 66, 72, 74, 82], 14, 104);
    console.log(`TEST-4...${result}`);
  
    result = driver([0, 1, 1, 1, 0, 0, 0, 1, 0, 1], 5, 0);
    console.log(`TEST-5...${result}`);
  
    result = driver([53, 63, 63], 2, 10);
    console.log(`TEST-6...${result}`);
  
    result = driver([-96, -38, -26, -46, 68, -36, 20, -18, -10, 52, 40, 94, -8, -64, 82, -22], 15, 34);
    console.log(`TEST-7...${result}`);
  
    result = driver([0, 0, 0, 0, 0, 1, 1], 3, 0);
    console.log(`TEST-8...${result}`);
  
    result = driver([99, 46, 48, 81, 27, 97, 26, 50, 77, 32, 45, 99, 46], 12, 1);
    console.log(`TEST-9...${result}`);
  
  };
  
  main();
question_info.extension: ts
question_info.entry_fn_name: findTheElementThatAppearsOnce
question_info.test_case_ids: 0 1 2 3 4 5 6 7 8 9
question_info.commands: tsc --target es2020 --lib es5,dom,es2015,es2020 __FILENAME__
question_info.commands: node __FILENAME__.js