A first punch circumferential ARTS

class Solution { public: int singleNumber(vector & Nums) {# if 0 // Method a: count here with additional space std :: sort (nums.begin (), nums.end ()); for (int i = 0; i <nums.size (); i + = 2) {if (i + 1> = nums.size () || nums [i] = nums [i + 1]) {return nums [i];!}} return 0; #else // ^ = 2. using the algorithm (the same is false, different true) int iRes = 0; for (int i = 0; i <nums.size (); i ++) {iRes ^ = nums [i];} return iRes; #endif}};