【CodeForces - 1084C】The Fair Nut and String(思维,组合数学)
题干:TheFairNutfoundastringss.ThestringconsistsoflowercaseLatinletters.TheNutisacuriousguy,sohewantstofindthenumberofstrictlyincreasingsequencesp1,p2,…,pkp1,p2,…,pk,suchthat:Foreachii(1≤i≤k1≤i≤k),spi=sp