CUIT ACM Personal Training 11.27(FM)A - Buggy Sor

探讨了BuggySorting算法的缺陷,通过分析错误冒泡排序实现,找到了导致该算法失效的输入反例,特别指出当输入数组长度大于3时,逆序数组即可构成反例。

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A - Buggy Sorting
Time Limit:2000MS     Memory Limit:262144KB     64bit IO Format:%I64d & %I64u

Description

Little boy Valera studies an algorithm of sorting an integer array. After studying the theory, he went on to the practical tasks. As a result, he wrote a program that sorts an array of n integers a1, a2, ..., an in the non-decreasing order. The pseudocode of the program, written by Valera, is given below. The input of the program gets number n and array a.

loop integer variable i from 1 to n - 1
    loop integer variable j from i to n - 1
        if (aj > aj + 1), then swap the values of elements aj and aj + 1

But Valera could have made a mistake, because he hasn't yet fully learned the sorting algorithm. If Valera made a mistake in his program, you need to give a counter-example that makes his program work improperly (that is, the example that makes the program sort the array not in the non-decreasing order). If such example for the given value of n doesn't exist, print -1.

Input

You've got a single integer n (1 ≤ n ≤ 50) — the size of the sorted array.

Output

Print n space-separated integers a1, a2, ..., an (1 ≤ ai ≤ 100) — the counter-example, for which Valera's algorithm won't work correctly. If the counter-example that meets the described conditions is impossible to give, print -1.

If there are several counter-examples, consisting of n numbers, you are allowed to print any of them.

Sample Input

Input
1
Output
-1



这个题的题意大概就说有人写了一个错误的冒泡排序,问你能否找出一个反例的输入,使得他的结果错误。
我们可以先来看看这个错误的冒泡排序,很容易发现,它每次的起始位置都在前移,也就是说比如一开始一串数字为4 3 2 1,第一次循环的时候起始位置是4,然后3与4进行交换,这串数字变成了3 4 2 1,然后依次交换之后变成了3 2 1 4。然而第二次循环的时候,他的起始位置数字不是3,而是2,那么3就永远不会被替换到了,所以最后结果肯定是错误的,所以可以看出,当我们的数字数量超过3个的时候,我们逆序排列输入,他的程序就会出错。而当只有一个数字和两个数字的时候,他的程序不进行交换,或者仅仅交换一次,那么我们就找不到反例,使得他的程序答案错误了。
所以AC代码如下;

#include<iostream>
using namespace std;

int main()
{
    int n;cin>>n;
    if(n==1||n==2) cout<<"-1"<<endl;
    else{for(int i=n;i>=1;i--) cout<<i<<" ";}
    cout<<endl;
    return 0;
}




(venv) PS E:\cuit一步到胃1\Flask_project> flask run Traceback (most recent call last): File "<frozen runpy>", line 198, in _run_module_as_main File "<frozen runpy>", line 88, in _run_code File "D:\python\cuit\venv\Scripts\flask.exe\__main__.py", line 7, in <module> sys.exit(main()) ~~~~^^ File "D:\python\cuit\venv\Lib\site-packages\flask\cli.py", line 1064, in main cli.main() ~~~~~~~~^^ File "D:\python\cuit\venv\Lib\site-packages\click\core.py", line 1363, in main rv = self.invoke(ctx) File "D:\python\cuit\venv\Lib\site-packages\click\core.py", line 1830, in invoke return _process_result(sub_ctx.command.invoke(sub_ctx)) ~~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^ File "D:\python\cuit\venv\Lib\site-packages\click\core.py", line 1226, in invoke return ctx.invoke(self.callback, **ctx.params) ~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ File "D:\python\cuit\venv\Lib\site-packages\click\core.py", line 794, in invoke return callback(*args, **kwargs) File "D:\python\cuit\venv\Lib\site-packages\click\decorators.py", line 93, in new_func return ctx.invoke(f, obj, *args, **kwargs) ~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^ File "D:\python\cuit\venv\Lib\site-packages\click\core.py", line 794, in invoke return callback(*args, **kwargs) File "D:\python\cuit\venv\Lib\site-packages\flask\cli.py", line 912, in run_command raise e from None File "D:\python\cuit\venv\Lib\site-packages\flask\cli.py", line 898, in run_command app = info.load_app() File "D:\python\cuit\venv\Lib\site-packages\flask\cli.py", line 313, in load_app app = locate_app(import_name, None, raise_if_not_found=False) File "D:\python\cuit\venv\Lib\site-packages\flask\cli.py", line 236, in locate_app return find_best_app(module) File "D:\python\cuit\venv\Lib\site-packages\flask\cli.py", line 64, in find_best_app app = app_factory() File "E:\cuit一步到胃1\Flask_project\app\__init__.py", line 50, in create_app from app.routes.user import user_bp File "E:\cuit一步到胃1\Flask_project\app\routes\user.py", line 15 db.session.commit() IndentationError: unexpected indent
最新发布
06-18
(venv) PS E:\cuit一步到胃1\Flask_project> flask db init Traceback (most recent call last): File "<frozen runpy>", line 198, in _run_module_as_main File "<frozen runpy>", line 88, in _run_code File "D:\python\cuit\venv\Scripts\flask.exe\__main__.py", line 7, in <module> sys.exit(main()) ~~~~^^ File "D:\python\cuit\venv\Lib\site-packages\flask\cli.py", line 1064, in main cli.main() ~~~~~~~~^^ File "D:\python\cuit\venv\Lib\site-packages\click\core.py", line 1363, in main rv = self.invoke(ctx) File "D:\python\cuit\venv\Lib\site-packages\click\core.py", line 1824, in invoke cmd_name, cmd, args = self.resolve_command(ctx, args) ~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^ File "D:\python\cuit\venv\Lib\site-packages\click\core.py", line 1871, in resolve_command cmd = self.get_command(ctx, cmd_name) File "D:\python\cuit\venv\Lib\site-packages\flask\cli.py", line 579, in get_command app = info.load_app() File "D:\python\cuit\venv\Lib\site-packages\flask\cli.py", line 313, in load_app app = locate_app(import_name, None, raise_if_not_found=False) File "D:\python\cuit\venv\Lib\site-packages\flask\cli.py", line 236, in locate_app return find_best_app(module) File "D:\python\cuit\venv\Lib\site-packages\flask\cli.py", line 64, in find_best_app app = app_factory() File "E:\cuit一步到胃1\Flask_project\app\__init__.py", line 50, in create_app from app.routes.user import user_bp File "E:\cuit一步到胃1\Flask_project\app\routes\user.py", line 15 db.session.commit() IndentationError: unexpected indent
06-18
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