Cod sursă (job #133347)

#include <fstream>
#include <cstdio>
#include <cstring>
using namespace std;

ofstream g("sqrt.out");

long n,i,j,v[3320],x,aux[3320],st[3321],ax,mij[3320],dr[3320],vv[3320];
char s[3010];

long compara(long a[],long b[])
{
    if (a[0]<b[0])
        return -1;
    else if (a[0]>b[0])
        return 1;
    for (int i=a[0];i>=1;i--)
        if (a[i]<b[i])
            return -1;
        else if (a[i]>b[i])
            return 1;
    return 0;
}

void add(long C[], long A[], long B[])
{
      int i, t = 0;
      for (i=1; i<=A[0] || i<=B[0] || t; i++, t/=10)
              C[i] = (t += A[i] + B[i]) % 10;
      C[0] = i - 1;
}




void mul(long A[], long B[])
{
      int i, j, t, C[3320];
      memset(C, 0, sizeof(C));
      for (i = 1; i <= A[0]; i++)
      {
              for (t=0, j=1; j <= B[0] || t; j++, t/=10)
                      C[i+j-1]=(t+=C[i+j-1]+A[i]*B[j])%10;
              if (i + j - 2 > C[0]) C[0] = i + j - 2;
      }
      memcpy(A, C, sizeof(C));
}

void div(long A[], long B)
{
      int i, t = 0;
      for (i = A[0]; i > 0; i--, t %= B)
              A[i] = (t = t * 10 + A[i]) / B;
      for (; A[0] > 1 && !A[A[0]]; A[0]--);
}

void sub(long A[], long B[])
{
      int i, t = 0;
      for (i = 1; i <= A[0]; i++) {
              A[i] -= ((i <= B[0]) ? B[i] : 0) + t;
              A[i] += (t = A[i] < 0) * 10;
      }
      for (; A[0] > 1 && !A[A[0]]; A[0]--);
}

long modul(long a)
{
    if (a<0)
        return -a;
    return a;
}
int main()
{
    freopen("sqrt.in","r",stdin);
    scanf("%s",&s);
    n=strlen(s);
    for (i=0;i<n;i++)
        v[i+1]=s[i]-'0';
    for (i=0;i<=n/2;i++)
    {
        ax=v[i];
        v[i]=v[n-i+1];
        v[n-i+1]=ax;
    }
    v[0]=n;

    if (n>3)
    {
        st[0]=n/2-1;
        st[n/2-1]=1;
        dr[0]=n/2+1;
        dr[n/2+1]=1;
    }
    else
    {
        st[0]=st[1]=1;
        dr[0]=6;
        dr[6]=1;
    }
    vv[1]=vv[0]=1;
    x=1;
    while (compara(st,dr)<=0)
    {
        if (mij[0]==16)
            mij[0]=16;
        if (mij[0]==100)
            mij[0]=100;
        add(mij,st,dr);
        div(mij,2);
        memcpy(aux, mij, sizeof(mij));
        if (modul(mij[0]*2-1-v[0])<=2)
        {
            mul(aux,mij);
            x=compara(aux,v);
        }
        else
        {
            if (mij[0]*2-1<v[0])
                x=-1;
            else
                x=1;
        }
        if (x==0)
            break;
        else if (x<0)
        {
            add(mij,mij,vv);
            memcpy(st,mij,sizeof(mij));
        }
        else
        {
            sub(mij,vv);
            memcpy(dr,mij,sizeof(mij));
        }
    }
    if (x==0)
    {
        for (i=mij[0];i>=1;i--)
            g<<mij[i];
    }
    else
    {
        for (i=dr[0];i>=1;i--)
            g<<dr[i];
    }
    g.close();
    return 0;
}