830. Positions of Large Groups

 1 class Solution 
 2 {
 3 public:
 4     vector<vector<int>> largeGroupPositions(string S) 
 5     {
 6         S.push_back(‘ ‘);
 7         int pre=0;
 8         int len=S.length();
 9         vector<vector<int>> res;
10         for(int i=0;i<len;i++)
11         {
12             if(S[i]!=S[pre])
13             {
14                 if(i-pre>2)
15                     res.push_back({pre,i-1});
16                 pre=i;
17             }
18         }
19         return res;
20     }
21 };