JavaSE：第十七章：编程测试题

long sum = 0;
for (int i = 1; i <= 20; i++) {
    long temp= 1;
    for (int j = 1; j <= i; j++) {
        temp *= j;
    }
    sum += temp;
}
System.out.println(sum);
123456789

public static void main(String[] args) {
        String string = "中国,国国哥,好帅是个大帅,哥哥";
        HashMap<Character, Integer> hashMap = new HashMap<>();
        while(string.length()>0) {
            Character c = string.charAt(0);
            string = string.substring(1);
            Integer integer = hashMap.get(c);
            if(integer == null ) {
                hashMap.put(c, 1);
            }else {
                hashMap.put(c, integer + 1);
            }
        }
        Set<Entry<Character, Integer>> entrySet = hashMap.entrySet();
        for (Entry<Character, Integer> entry : entrySet) {
            System.out.println(entry);
        }
}
123456789101112131415161718

哥=3
帅=2
大=1
个=1
,=3
中=1
国=3
好=1
是=1
123456789