求解决( Java )

[sunshinel]

20 个人围成一圈，每个人背上都贴有一个编号，依次为 1、2、...、20，现在从编号为 1 的人开始，从 1 依次递增报数，凡是报的数是 3 的倍数人离开圈子，剩下的人继续往下报数，问最后留下的那个人的编号是多少？请编写程序解决此问题。

[picasso2501]

@xiangyuecn 22 轮会杀掉 22 个人。（ 1 万个？）

[georgetso]

https://baike.baidu.com/item/约瑟夫问题

[lyusantu]

```
import java.util.ArrayList;
import java.util.List;

public class Test {

public static void main(String[] args) {
List<Integer> list = new ArrayList<Integer>();
for (int i = 0; i < 20; i++) {
list.add((i + 1));
}
numberOff(list);
System.out.println(list.get(0));
}

public static List<Integer> numberOff(List<Integer> list) {
for (int i = 0; i < list.size(); i++) {
list.set(i, list.get(i) + 1);
if (list.get(i) % 3 == 0) {
list.remove(i);
if (list.size() == 1)
break;
else
--i;
}
}
return list.size() > 1 ? numberOff(list) : list;
}
}

```

[lyusantu]

从 1 开始递增报数，最大数为 20，最后剩下的数结果也是 20

[xiangyuecn]

@picasso2501 #21 我那设定的 n=10000，需要循环报数 22 轮。如果 n=20 跟楼主一样的初始条件的话，是 7 轮，结果是 20

[Windsooon]

别想太多，循环计算一下就好（ python3 ）

class solution:
def josephus(self, n, k):
last = 0
for i in range(1, n+1):
last = (last+k) % i
return last

[Andiry]

一个摆明了作业不会做想偷懒的人，你们上来直接贴答案，这样好吗？

[sunjiayao]

package main

import (
"strconv"
)

type People struct {
index int64
next *People
parent *People
}

func initPeople(first *People,people *People){
nextPeople := new(People)
nextPeople.index = people.index+1
nextPeople.parent = people
people.next = nextPeople

if nextPeople.index==20{
nextPeople.next = first
first.parent = nextPeople
return
}
initPeople(first,nextPeople)
}


func main() {

people := new(People)
people.index = 1
initPeople(people,people)
var count int64 = 0
for people.next != people{
count ++
if count % 3 ==0{
people.next.parent = people.parent
people.parent.next = people.next
}
people = people.next
}
println("finally number :"+strconv.FormatInt(people.index,10)+"; for count is :"+strconv.FormatInt(count,10))

}



//没用 java，不过思路是一样的。结果是 20 吗？

[feeeeeef]

Let's begin!
I am 3,killed by 3
I am 6,killed by 6
I am 9,killed by 9
I am 12,killed by 12
I am 15,killed by 15
I am 18,killed by 18
The 1 round end.
I am 1,killed by 21
I am 5,killed by 24
I am 10,killed by 27
I am 14,killed by 30
I am 19,killed by 33
The 2 round end.
I am 4,killed by 36
I am 11,killed by 39
I am 17,killed by 42
The 3 round end.
I am 7,killed by 45
I am 16,killed by 48
The 4 round end.
I am 8,killed by 51
The 5 round end.
I am 2,killed by 54
The 6 round end.
I am 13,killed by 57
The 7 round end.
Game over!
I am 20,winner!
58

[unforgiven]

这题我在一家公司面试做过，我当时的解决思路是将 1-n 放到一个 list 里面，建一个 while 循环，再建一个 for 循环，每当 i 除以 3 的余数为零的时候，list 里面删除这个 index 的元素，直到剩最后一个元素

[sunshinel]

@Andiry 实在是能力有限，初学 JAVA。也想了做不出来呀！

[lyusantu]

@sunshinel 上一个回复的解答是不对的，问题是“问最后留下的那个人的编号”而非最后留下的数字，所以更正后的代码 如下：

import java.util.ArrayList;
import java.util.List;

public class Test {

public static void main(String[] args) {
List<Integer> list = new ArrayList<Integer>();
for (int i = 0; i < 20; i++) {
list.add((i + 1));
}
numberOff(list);
System.out.println("最后留下的人的编号为：" + numberOff(list));
}

public static Integer numberOff(List<Integer> list) {
int start = 0;
while (list.size() > 1) {
for(int i = 0; i < list.size(); i++){
if (++start % 3 == 0)
list.remove(i);
if(list.size() == 1)
break;
--i;
}
}
return list.get(0);
}
}

[jinhan13789991]

@lyusantu 为什么 留下来的是始终是最后一个 你的代码

[lyusantu]

@jinhan13789991 因为其他数字都被淘汰掉了