 设计一个可以支持无限精度的计算器；支持+、-、*、/四种运算,至少一种运算运用分支法, 现＋、-法用常规法，时间复杂度为O(n), *法可以使用常规法、二分法、FFT法- design can support an infinite precision calculator +,-,*,/ four computing support, computing at least one branch of law to use, =