题解 | #阿拉伯数字转中文#

 public static String nextGreaterElement(long n) {
            Map<Integer, String> num2Chn = new HashMap<>();
            num2Chn.put(0, "零");
            num2Chn.put(1, "一");
            num2Chn.put(2,"二");
            num2Chn.put(3,"三");
            num2Chn.put(4, "四");
            num2Chn.put(5,"五");
            num2Chn.put(6,"六");
            num2Chn.put(7,"七");
            num2Chn.put(8,"八");
            num2Chn.put(9,"九");
            num2Chn.put(10,"十");
            num2Chn.put(100,"百");
            num2Chn.put(1000,"千");
            if(n==0) return num2Chn.get(0);
            StringBuilder sb = new StringBuilder();
            Stack<String> stack = new Stack<>();
            int i = 1;
            long pre = -1;
            while(n>0){
                int t = (int) (n%10);
                n /=10;
                if(t>0 || (t == 0 && pre != 0 && i>1)) {
                    String s = num2Chn.get(t);
                    if(i%4 == 2 && t>0){
                        sb.append(num2Chn.get(10));
                    }else if(i%4==3&& t>0){
                        sb.append(num2Chn.get(100));
                    }else if(i%4 == 0&& t>0){
                        sb.append(num2Chn.get(1000));
                    }
                    sb.append(s);
                }
                pre = t;
                i++;
                if(i == 5 || i == 9 || n<=0){
                    sb.reverse();
                    String s = sb.toString();
                    if(s.startsWith("一十")) s = s.substring(1);
                    stack.push(s);
                    i = 1;
                    pre = -1;
                    sb = new StringBuilder();
                }
            }
            StringBuilder res = new StringBuilder();
            while(!stack.isEmpty()){
                res.append(stack.pop());
                if(stack.size() == 2){
                    res.append("亿");
                }else if(stack.size() == 1 && res.charAt(res.length()-1) != '亿'){
                    res.append("万");
                }
            }
            return res.toString();
        }


每四个数字一组，分别处理，因为 个十百千/ 万 十万 百万 千万/ 亿 十亿 百亿 千亿 都是四个数字一组

这篇文章的思路很好可以看下，我的思路也借鉴这里

https://juejin.cn/post/7056769354452434975

测试用例也借鉴了这篇博客

 System.out.println(Solution.cal(0));
        System.out.println(Solution.cal(1));
        System.out.println(Solution.cal(10));
        System.out.println(Solution.cal(15));
        System.out.println(Solution.cal(25));
        System.out.println(Solution.cal(100));
        System.out.println(Solution.cal(115));
        System.out.println(Solution.cal(234));
        System.out.println(Solution.cal(999));
        System.out.println(Solution.cal(1501));
        System.out.println(Solution.cal(1006));
        System.out.println(Solution.cal(9905));
        System.out.println(Solution.cal(20394));
        System.out.println(Solution.cal(100001));
        System.out.println(Solution.cal(100000));
        System.out.println(Solution.cal(100101822));
        System.out.println(Solution.cal(123412341234L));
        System.out.println(Solution.cal(10000000000L));

零
一
十
十五
二十五
一百
一百一十五
二百三十四
九百九十九
一千五百零一
一千零六
九千九百零五
二万零三百九十四
十万零一
十万
一亿零一十万一千八百二十二
一千二百三十四亿一千二百三十四万一千二百三十四
一百亿