note difference String Transformation 1 String Transformation 2 Koa in version letter y Koa select strictly great alphabetically x read statement well understand you hack problem independentlykoa Koala string A b length n ABn consist 20 lowercase english alphabet letter ie tin Koa select subset position p_1 p_2 ldot p_k k ge 1 1 le p_i le n p_i neq p_j neq j a a_p_1 a_p_2 ldots A_p_k x ie letter position equal letter x select letter y 20 lowercase letter English alphabet yx ie letter y strictly great alphabetically x set letter position p_1 p_2 ldot p_k letter y more formally 1 le le k Koa set A_p_i y Note modify letter stre AKoa want know small number move string equal A b determine way equal help