Points: $350$ points

问题陈述

给定一个字符串 $S$。找出通过执行以下操作恰好一次可以得到的字符串数量。

• 设 $N$ 为 $S$ 的长度。选择一对整数 $(i,j)$，使得 $1\leq i<j\leq N$ 并交换 $S$ 中的第 $i$ 个和第 $j$ 个字符。

可以证明，在这个问题的约束条件下，你总是可以执行这个操作。

以上为大语言模型 kimi 翻译，仅供参考。

Problem Statement

You are given a string $S$. Find the number of strings that can result from performing the following operation exactly once.

• Let $N$ be the length of $S$. Choose a pair of integers $(i,j)$ such that $1\leq i<j\leq N$ and swap the $i$-th and $j$-th characters of $S$.

It can be proved that you can always perform it under the constraints of this problem.

Constraints

• $S$ is a string of length between $2$ and $10^6$, inclusive, consisting of lowercase English letters.

Input

The input is given from Standard Input in the following format:

$S$

Output

Print the number of strings that can result from performing the operation in the problem statement exactly once on $S$.

Sample Input 1

abc

Sample Output 1

3

The length of $S$ is $3$, so $1\leq i<j\leq 3$ is satisfied by three pairs of integers $(i,j)$: $(1,2)$, $(1,3)$, and $(2,3)$.

• Swapping the $1$-st and $2$-nd characters of $S$ results in $S$ being bac.
• Swapping the $1$-st and $3$-rd characters of $S$ results in $S$ being cba.
• Swapping the $2$-nd and $3$-rd characters of $S$ results in $S$ being acb.

Therefore, the operation on abc results in one of the three strings: bac, cba, and acb, so print $3$.

Sample Input 2

aaaaa

Sample Output 2

1

Swapping any two characters results in $S$ remaining aaaaa. Thus, only one string can result from the operation.

update @ 2024/5/16 17:16:45