odeforces Round #144 (Div. 2) B

http://codeforces.com/contest/233/problem/B

s(x)最大为81.所以x*(x+s(x))==n假如有x存在，则x必然小于sqrt(n)。且大于sqrt(n)-82。。

#include <iostream>
#include <cstdio>
#include <cstring>
#include <algorithm>
#include <cmath>

using namespace std;

long long n,ans;

int getsum(long long x)
{
    int s=0;
    while(x)
    {
        s+=x%10;
        x/=10;
    }
    return s;
}

int main()
{
    while(~scanf("%I64d",&n))
    {
        ans=-1;
        long long tmp=(long long ) sqrt(n);
        long long i=(tmp-82>0?tmp-82:1);
        for(;i<=tmp;i++)
            if(i*i+i*getsum(i)==n)
            {
                ans=i;
                break;
            }
        printf("%I64d\n",ans);
    }
    return 0;
}