题目描述

A string $s$ of length $n$ , consisting of lowercase letters of the English alphabet, is given.

You must choose some number $k$ between $0$ and $n$ . Then, you select $k$characters of $s$ and permute them however you want. In this process, the positions of the other $n-k$ characters remain unchanged. You have to perform this operation exactly once.

For example, if $s=\texttt{"andrea"}$ , you can choose the $k=4$ characters $\texttt{"a_d_ea"}$ and permute them into $\texttt{"d_e_aa"}$ so that after the operation the string becomes $\texttt{"dneraa"}$ .

Determine the minimum $k$ so that it is possible to sort $s$ alphabetically (that is, after the operation its characters appear in alphabetical order).

输入格式

The first line contains a single integer $t$ ( $1 \le t \le 1000$ ) — the number of test cases. Then $t$ test cases follow.

The first line of each test case contains one integer $n$ ( $1 \le n \le 40$ ) — the length of the string.

The second line of each test case contains the string $s$ . It is guaranteed that $s$ contains only lowercase letters of the English alphabet.

输出格式

For each test case, output the minimum $k$ that allows you to obtain a string sorted alphabetically, through the operation described above.

输入输出样例

输入 #1

4
3
lol
10
codeforces
5
aaaaa
4
dcba

输出 #1

2
6
0
4

分析

要判断将字符串进行排序需要移动几个字符,自然只需要判断排序后的字符串和原字符串的差异即可。依次扫描原字符串和排序后的字符串的每一个字符,如果不同则表示原字符串的这一个字符需要与目标字符进行对换,此时累加答案即可。

可以把字符转为数字方便判断,时间复杂度 $O(n\log n)$

代码

#include<bits/stdc++.h>
using namespace std;
int t,n;
char a[51];
int c[51],b[51];
int main(){
    scanf("%d",&t);
    while(t--){
        scanf("%d",&n);
        for(int i=1;i<=n;i++)cin>>a[i],c[i]=a[i]-96,b[i]=c[i];
        int ans=0;
        sort(b+1,b+1+n);
        for(int i=1;i<=n;i++)if(c[i]!=b[i])ans++;
        printf("%d\n",ans);
    }
}
最后修改:2021 年 08 月 04 日 10 : 03 AM
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