下面Python函数nGram()用于逐一从字符串中截取n个字符，如：nGram("ABCDEF",2)将逐一截取为AB、BC、CD、DE、EF，如：nGram("ABCDEF",3)将逐一截取为ABC、BCD、CDE、DEF，并统计每种截取的数量，横线处应填入代码是
def nGram(S, n):
Result = {}#保存截取字符串及其数量
for i in range(________________):
nChar = ________________
Result[nChar] = Result.get(nChar, 0) + 1
return Result
