表示输入字符串的长度，i1表示当前分析到的字符的下标,flag表示当前是否识别新的字符 //n表示初始的推导式长度为6，故其下标为5-That the length of input string, i1, said the current analysis to the character subscr ipt, flag indicated whether the current identification of new characters// n-type is deduced t