BBuBBBlesort!

这题是猜的…
给你一个不重复序列,有两种操作方式,一种是三个一起翻转,一种是两个一起翻转,猜了一下,好像如果是3个一起,那么只有左右两边会互换,如果一个点距他该在的地方位置是奇数,那就很尴尬,每次2个的距离改变,永远都没用,所以必须要一次两个翻转,ans = num/2+num&1.

#include <iostream>
#include <algorithm>
#include <map>
using namespace std;
#define debug(x) std::cerr << #x << " = " << (x) << std::endl
typedef long long LL;
const int MAXN = 1e5+17;
int a[MAXN],b[MAXN];
map<int,int > mp;
int main(int argc ,char const *argv[])
{
    #ifdef noob
    freopen("Input.txt","r",stdin);freopen("Output.txt","w",stdout);
    #endif      
    int n,ans=0;
    cin>>n;
    for (int i = 0; i < n; ++i)
    {
        cin>>a[i];
        b[i]=a[i];
    }
    sort(b, b+n);
    for (int i = 0; i < n; ++i)
    {
        mp[b[i]] = i+1;
    }
    for (int i = 0; i < n; ++i)
    {
        if(abs(i+1-mp[a[i]])&1) ans++;
    }
    cout<<ans/2+(ans&1)<<endl;
    return 0;   
}