text: // Given a non-empty array of integers, every element appears twice except for one. Find that single one.
  
  // Note:
  
  // Your algorithm should have a linear runtime complexity. Could you implement it without using extra memory?
  
  // Example 1:
  
  // Input: [2,2,1]
  // Output: 1
  // Example 2:
  
  // Input: [4,1,2,1,2]
  // Output: 4
  
  /**
   * @param {number[]} nums
   * @return {number}
   */
  var singleNumber = function(nums) {
      let retObj = {};
      for(let index = 0; index < nums.length; index++) {
          if(retObj[nums[index]]){
              delete retObj[nums[index]];
          } else {
              retObj[nums[index]] = true;
          }
      }
      return Object.keys(retObj)[0];
      
  };