一个排列问题 - 题目

#1435. 一个排列问题

统计

AI Translation — This statement was translated using AI and may contain inaccuracies. Please refer to the original statement if in doubt.

Zenyk 有一个包含 $1$ 到 $n$ 的排列。他的任务是将该排列排序，并且他必须恰好交换每一对整数各一次。

你能帮他完成这个任务吗？

输入格式

第一行包含一个整数 $n$ ($2 \le n \le 1000$)。第二行包含一个 $1$ 到 $n$ 之间的整数排列 $P$。

输出格式

如果无法将排列排序，输出 “no”。否则，输出 $\frac{n(n-1)}{2}$ 行，每行描述在对应步骤中需要交换的两个数值（而非下标）。

样例

样例输入 1

4
3 2 4 1

样例输出 1

样例输入 2

3
1 3 2

样例输出 2

1 3
3 2
1 2

样例输入 3

2
1 2

样例输出 3

no

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