minFlips.cpp

class LightSwitchingPuzzle {
    public:
    int minFlips(string state) {
      int ans=0;
      for(int i=0;i<state.size();i++)
        {
          if(state[i]=='Y')
            {
              ans++;
              for(int j=i;j<state.size();j+=(i+1))
                {
                  if(state[j]=='N')
                    state[j]='Y';
                  else
                    state[j]='N';
                }
            }
        }

      return ans;
    }
};