Plates Between Candles

Given a string of '*' (plates) and '|' (candles), answer many queries [l,r] by counting plates that lie strictly between at least one candle to their left and one to their right inside the substring (i.e., between the leftmost and rightmost candle in the range). The algorithmic challenge is to preprocess the string (e.g., nearest-candle indices and prefix sums) so each query can be answered efficiently.