p1459 Sorting a Three-Valued Sequence

如果将1和3都放到正确的位置，2自然也在正确的位置。那么统计1,2,3的数量num1,num2,num3。再看前num1个数有几个（设x个）不是1，那么x个1肯定要移。设前num1个数有y个3，最后num3个数有z个1，那么这个过程中，最多能将min(y,z)个3移到正确位置。剩下num3-min(y,z)个3也必须移到最后num3个位置

#include <iostream>

#include <cstdio>

#include <cmath>

#include <algorithm>

#include <vector>

#include <iomanip>

#include <cstring>

#include <map>

#include <queue>

#include <set>

#include <cassert>

#include <stack>

#define mkp make_pair

using namespace std;

const double EPS=1e-;

typedef long long lon;

const lon SZ=,INF=0x7FFFFFFF;

int arr[SZ];

int main()

{

    std::ios::sync_with_stdio();

    //freopen("d:\\1.txt","r",stdin);

    lon casenum;

    //cin>>casenum;

    //for(lon time=1;time<=casenum;++time)

    {

        int n;

        cin>>n;

        for(int i=;i<=n;++i)cin>>arr[i];

        int num1=count(arr+,arr++n,);

        int num2=count(arr+,arr++n,);

        int num3=count(arr+,arr++n,);

        int x=,y=,z=,w=;

        for(int i=;i<=num1;++i)

        {

            if(arr[i]!=)++x;

            if(arr[i]==)++z;

        }

        for(int i=num1+num2+;i<=n;++i)

        {

            if(arr[i]!=)++y;

            if(arr[i]==)++w;

        }

        //cout<<num1<<" "<<num2<<" "<<num3<<endl;

        //cout<<x<<" "<<y<<" "<<z<<endl;

        cout<<(x+y-min(z,w))<<endl;

    }

    return ;

}