Cod sursă (job #77207)

#include <cstdio>
#include <algorithm>
#define Nmax 200000+10
#define st first
#define dr second

using namespace std;

pair <int,int> fiu[Nmax];
int i,n,nr,x,rad,t,ant;
bool sel[Nmax];

void ord(int x)
{
    if (fiu[x].st==-1 || sel[fiu[x].st])
    {
        if (!sel[x]) fiu[x].st=ant, fiu[ant].dr=x, sel[x]=true, ant=x;
    }
    else ord(fiu[x].st);



    if (fiu[x].dr==-1 || sel[fiu[x].dr]) ;
    else
    if (fiu[x].dr)
    {
        if (!sel[x]) fiu[x].st=ant, fiu[ant].dr=x, sel[x]=true, ant=x;
        ord(fiu[x].dr);
    }



}

int main()
{
    freopen("pointeri.in","r",stdin);
    freopen("pointeri.out","w",stdout);

    scanf("%d %d", &n, &rad);
    for (i=0; i<n; ++i)
    {
        scanf("%d", &fiu[i].st);
    }
    for (i=0; i<n; ++i)
    {
        scanf("%d", &fiu[i].dr);
    }

    nr=0; x=rad; ant=-1;
    ord(x);

    for (i=0; i<n; ++i)
        if (fiu[i].st==-1)
            {
                printf("%d\n", i);
                break;
            }
    for (i=0; i<n; ++i) printf("%d ", fiu[i].st);
    printf("\n");
    for (i=0; i<n; ++i) printf("%d ", fiu[i].dr);







    return 0;
}