# SkyWT

#### 我们的征途是星辰大海

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Linux 下有些时候我们运行一个进程需要一直挂着（这就是 VPS 的意义啊……），这时候需要把前台进程放到后台去。一般可以用 screen，但是如果这种后台进程挂多了，每个都开一个 session 会很不方便。前几天配置 aria2 的时候看到一个神奇的操作：可以配置成一个 service，直接 service aria2c start/stop/restart 就可以了！

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2019.10.09 Upd：这篇文章弃坑啦，以后直接放在 Lab 页面里了。

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## Description

Ivan wants to make a necklace as a present to his beloved girl. A necklace is a cyclic sequence of beads of different colors. Ivan says that necklace is beautiful relative to the cut point between two adjacent beads, if the chain of beads remaining after this cut is a palindrome (reads the same forward and backward).

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## Description

Yaroslav has n points that lie on the $Ox$ axis. The coordinate of the first point is $x_1$, the coordinate of the second point is $x_2$, ..., the coordinate of the n-th point is — $x_n$. Now Yaroslav wants to execute $m$ queries, each of them is of one of the two following types:

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## Description

In mathematical terms, the sequence $F_n$ of Fibonacci numbers is defined by the recurrence relation

$$F_1 = 1; F_2 = 1; F_n = F_{n - 1} + F_{n - 2} (n > 2)$$

DZY loves Fibonacci numbers very much. Today DZY gives you an array consisting of n integers: $a_1, a_2, \dots, a_n$. Moreover, there are $m$ queries, each query has one of the two types:

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$$C[i,j]=\sum_{k=1}^{b} A[i,k]\ast B[k,j]$$

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## 引言

Bitset 是一种利用对布尔数组压位存储的方法，达到优化时间常数、空间常数的目的的黑科技。利用 Bitset，可以方便地对布尔数组进行按位逻辑运算，优化 32 或 64 的常数。在某些素质极差的卡常题中运用会有奇效。

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## Description

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1. 堆排序、快速排序、希尔排序、直接选择排序不是稳定的排序算法；
2. 基数排序、冒泡排序、直接插入排序、折半插入排序、归并排序是稳定的排序算法。

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