2、次迭代同时取下一个数值。AlltheVusersuseKiminthefirstiteration,Davidintheseconditeration,Michaelinthethirditeration,etc.2. EachOccurrence所有用户每次遇到同时取下一个数值,即使在同一个迭代。AlltheVusersuseKiminthefirstoccurrence,Davidinthesecondoccurrence,Michaelinthethirdoccurrence,etc.3. Once