text: /* eslint guard-for-in: ["error", true] */
  
  /**
   * Given array of integers, find two elements that appear once
   * Time/Space complexity: O(N); Constant space requires XOR knowledge
   * @param  {number[]} arr
   * @return {number}
   */
  function findIndividualElements(arr) {
    const hash = {};
    const ret = [];
  
    arr.forEach(element => {
      if (!hash[element]) {
        hash[element] = 1;
      } else {
        hash[element] += 1;
      }
    });
  
    for (const k in hash) {
      if (hash[k] === 1) {
        ret.push(k);
      }
    }
  
    return ret;
  }
  
  // findIndividualElements([2, 4, 6, 8, 10, 2, 6, 10]); // ['4', '8']
  