class Solution {
public:
vector<vector<int>> largeGroupPositions(string s) {
vector<vector<int>> res;
int num = 1;
int n = s.size();
for(int i=0;i<n;i++){
if(i == n-1 || s[i]!=s[i+1]){
if(num >= 3 )
{
res.push_back({i-num+1,i});
}
num = 1;
}
else num++;
}
return res;
}
};