LeetCode 217. Contains Duplicate

 1 class Solution {
 2 public:
 3     bool containsDuplicate(vector<int>& nums) {
 4         sort(nums.begin(), nums.end());
 5         int i = 0, size = nums.size();
 6         while(i < size - 1){
 7             if(nums[i] == nums[i + 1])
 8                 return true;
 9             ++i;
10         }
11         return false;
12     }
13 };

 1 class Solution {
 2 public:
 3     bool containsDuplicate(vector<int>& nums) {
 4         set<int> set_num;
 5         for(int i = 0; i < nums.size(); ++i){
 6             if(!set_num.insert(nums[i]).second) return true; 
 7         }
 8         return false;
 9     }
10 };