I recently participated in the div 3 contest and tried to solve problem D : Distinct character queries with Square Root Decomposition using a 2D array like block[denoting_which_block][charfreq] and it passed all the 50 odd pretests during contest and I was over the moon because I just recently learned this concept. But today morning, it was hacked sadly :( And I want to know why the solution fails? Should I have used seg/fenwick? This is my submission The thing is we keep looking for a small indication to denote our improvement every single time and feels bad to not grow despite practise

Thanks :)