Codeforces Round #280 (Div. 2)A B C

A - Vanya and Cubes:

#include
#include
#include

using namespace std;

typedef __int64 ll;
const int N = 10005;

ll a[N];

int main()
{
    a[0] = 0;
    for( ll i = 1; i <= 10000; i++ )
    {
        a[i] = i * (i+1) / 2 + a[i-1];
    }
    ll n;
    while(~scanf("%I64d", &n))
    {
        int ans = lower_bound(a, a+10000, n) - a;
        if( a[ans] > n )
            ans--;
        printf("%d\n", ans);
    }
    return 0;
}

B - Vanya and Lanterns:

#include
#include
#include

using namespace std;

#define N 1005

double a[N];

int main()
{
    int n;
    double L;
    while(~scanf("%d%lf", &n, &L))
    {
        double l = 1e9 + 10, r = 0, maxx = 0;
        for( int i = 1; i <= n; i++ )
        {
            scanf("%lf", &a[i]);
            l = min(l, a[i]);
            r = max(r, a[i]);
        }
        sort(a+1, a+1+n);
        for( int i = 2; i <= n; i++ )
        {
            maxx = max(maxx, a[i] - a[i-1]);
        }
        double ans = max( maxx / 2, max(l, L - r));
        printf("%.10f\n", ans);
    }
    return 0;
}

C - Vanya and Exams 

#include 
#include 
using namespace std;

typedef __int64 LL;
const int size = 100010;
struct data
{
    int a , b;
}node[size];

bool cmp( const data p , const data q )
{
    return p.b < q.b;
}

int main()
{
    int r;
    LL ans , sum , temp , n , avg;
    while( ~scanf("%I64d %d %I64d",&n,&r,&avg) )
    {
        sum = 0;
        ans = 0;
        for( int i = 0 ; i= avg*n )
        {
            printf( "0\n" );
        }
        else
        {
            sum = avg*n - sum;
            sort( node , node+n , cmp );
            for( int i = 0 ; i 0 )
                {
                    temp = min( (LL)r-node[i].a , sum );
                    sum -= temp;
                    ans += (LL)(temp * node[i].b);
                }
            }
            printf( "%I64d\n",ans );
        }
    }
    return 0;
}