830. Positions of Large Groups

class Solution 
{
public:
    vector<vector<int>> largeGroupPositions(string S) 
    {
        S.push_back(' ');
        int pre=0;
        int len=S.length();
        vector<vector<int>> res;
        for(int i=0;i<len;i++)
        {
            if(S[i]!=S[pre])
            {
                if(i-pre>2)
                    res.push_back({pre,i-1});
                pre=i;
            }
        }
        return res;
    }
};

这题比较简单了，没啥说的，问题不大