USACO 2.1.3 Sorting A Three-Valued Sequence

USACO 2.1.3 Sorting A Three-Valued Sequence

/**/ /*
ID: lorelei3
TASK: sort3
LANG: C++
*/

#include  < fstream >
#include  < iostream >
#include  < algorithm >

using   namespace  std;

const   int  MAX  =   1005 ;

int  first[MAX], second[MAX];
int  n;

int  main() {

    int i,j, npairs=0, ntriples=0, nswap=0;

    ifstream in("sort3.in");
    ofstream out("sort3.out");

    in>>n;
    for(i=0; i<n; ++i){
        in>>first[i];
        second[i]=first[i];
    }

    sort(second, second+n);

    for(i=0; i<n; ++i)
        for(j=0; j<n; ++j)
            if(first[i]!=second[i] && first[j]!=second[j]
                && first[i]==second[j] && second[i]==first[j]){
                first[i]  = second[i];
                first[j] = second[j];
                npairs++;
            }

    for(i=0; i<n; ++i)
        if(first[i]!=second[i])
            ntriples++;
    
    nswap = npairs + ntriples/3 *2;

    out<<nswap<<endl;
    return 0;
}