List实现大整数减法

    @Test
    public void bigIntReduceTest(){
        System.out.println(bigIntReduce("101312312735600","1323653943500"));
    }

    public String bigIntReduce(String num1,String num2){
        List<String> strList1 = new LinkedList<>(Arrays.asList(num1.split("")));
        List<String> strList2 = new LinkedList<>(Arrays.asList(num2.split("")));
        List<Integer> list1 = new LinkedList<>();
        List<Integer> list2 = new LinkedList<>();
        CollectionUtils.collect(strList1, input -> Integer.valueOf(input.toString()),list1);
        CollectionUtils.collect(strList2, input -> Integer.valueOf(input.toString()),list2);
        Collections.reverse(list1);
        Collections.reverse(list2);
        return reduceList(list1,list2);
    }
    private String reduceList(List<Integer> list1,List<Integer> list2){
        StringBuilder sb = new StringBuilder();
        List<Integer> resList ;
        //位数多的作为被减数
        if (list1.size()>list2.size()){
            resList = reduce(list1,list2);
        }else {
            resList = reduce(list2,list1);
            //位数少的-位数多的加负号
            sb.append("-");
        }
        //去除高位的0
        for(int len=resList.size()-1,i=len;i>=0;i--) {
            if (resList.get(i) == 0) {
                resList.remove(i);
            }else {
                break;
            }
        }
        //翻转
        Collections.reverse(resList);
        for (int aResList : resList) {
            sb.append(aResList);
        }
        return sb.toString();
    }
    private List<Integer> reduce(List<Integer> list1,List<Integer> list2){
        int len1 = list1.size();
        int len2 = list2.size();
        int len = len1>len2?len1:len2;
        List<Integer> list3 = new LinkedList<>();
        for(int i=0;i<len;i++) {
            if (len2 > i) {
                int res = list1.get(i) - list2.get(i);
                if (res < 0) {
                    res += 10;
                    if (i + 1 < len1) {
                        list1.set(i + 1, list1.get(i + 1) - 1);
                    }
                }
                list3.add(res);
            } else {
                if(list1.get(i)<0){
                    list1.set(i, list1.get(i) + 10);
                    list1.set(i + 1, list1.get(i + 1) - 1);
                }
                list3.add(list1.get(i));
            }
        }
        return list3;
    }