来自Codefighters:Note:WriteasolutionwithO(n)timecomplexityandO(1)additionalspacecomplexity,sincethisiswhatyouwouldbeaskedtododuringarealinterview.Givenanarrayathatcontainsonlynumbersintherangefrom1toa.length,findthefirstduplicatenumberforwhichthesecondoccurrencehastheminimalindex.Inotherwords,ifth