三值排序——usaco

求最小排序交换次数

贪心做

#include<stdio.h>
#include<algorithm>
#include<iostream>
using namespace std;

int b[1009],a[1009];

int min(int a,int b)
{
    if(a>b)return b;
    else return a;
}
int max(int a,int b)
{
    if(a>b)return a;
    else return b;
}

int main()
{
    int n;
    int add[6];
    while(scanf("%d",&n)!=EOF)
    {
        memset(add,0,sizeof(add));

        int i;
        for(i=0;i<n;i++)
        {
            scanf("%d",&a[i]);
            b[i]=a[i];
        }

        sort(&a[0],&a[n]);
        int all=0;
        for(i=0;i<n;i++)
        {
            if(a[i]==1&&b[i]==2)
                add[0]++;
        else    if(a[i]==2&&b[i]==1)
                add[1]++;
        else    if(a[i]==2&&b[i]==3)
                add[2]++;
        else    if(a[i]==3&&b[i]==2)
                add[3]++;
        else    if(a[i]==1&&b[i]==3)
                add[4]++;
        else    if(a[i]==3&&b[i]==1)
                add[5]++;
        }
        all=min(add[0],add[1])+min(add[2],add[3])+min(add[4],add[5]);
        all+=(max(add[0],add[1])-min(add[0],add[1])+max(add[2],add[3])-min(add[2],add[3])+max(add[4],add[5])-min(add[4],add[5]))/3*2;
        printf("%d\n",all);
    }
}