Submission #1001008

#	Time	Username	Problem	Language	Result	Execution time	Memory
1001008		amine_aroua	A Difficult(y) Choice (BOI21_books)	C++17	60 / 100	2 ms	2136 KiB

books

#include <bits/stdc++.h>
using namespace std;
#define intt long long
#define forr(i , x , y) for(int i = x ;i <= y;i++)
#define pb push_back
#define fore(i , n) for(int i = 0 ; i <n;i++)
/**
 * skims through the i-th book and returns its difficulty x_i (1 <= i <= N).
 */
long long skim(int);

/**
 * buys your selection of books. This function has to be called with
 * v = {i_1, ..., i_K} (1 <= i_1, ..., i_K <= N) where the i_j's are pairwise
 * distinct and satisfy A <= x_{i_1} + ... + x_{i_K} <= 2 A.
 */
void answer(std::vector<int>);

/**
 * states that it is impossible to buy a set of K books with the desired difficulty.
 */
void impossible();
intt get(int i , vector<intt> &x)
{
    if(x[i] == -1)
        return x[i] = skim(i);
    return x[i];
}
void solve(int n, int k, long long a, int s)
{
    vector<intt> x(n + 1 , -1);
    vector<intt> pref(n + 1);
    vector<int> ans;
    forr(i , 1 , k - 1)
    {
        pref[i] = pref[i - 1] + get(i , x);
    }
    if(pref[k - 1] + get(k , x) > 2ll * a)
    {
        impossible();
    }
    intt h = 0;
    for(int i = n ; i > n - k;i--)
        h+=get(i , x);
    if(h < a)
    {
        impossible();
    }
    int l = 0 , r = n;
    while(l + 1 < r)
    {
        int mid = (l + r)/2;
        if(get(mid , x) >= a)
        {
            r = mid;
        }
        else
            l = mid;
    }
    if(get(r , x) >= a && r >= k && get(r , x) + pref[k - 1] <= 2ll*a)
    {
        forr(i , 1, k - 1)
            ans.pb(i);
        ans.pb(r);
        answer(ans);
        return ;
    }
    int lo = k, hi = r + 1;
    while(lo + 1 < hi)
    {
        int mid = (lo + hi)/2;
        intt sm= 0;
        forr(i , mid - k + 1 , mid)
        {
            sm+=get(i , x);
            if(sm > 2ll * a)
            {
                break;
            }
        }
        if(a <= sm && sm <= 2ll * a)
        {
            forr(i , mid - k + 1 , mid)
                ans.pb(i);
            answer(ans);
            return;
        }
        if(sm > 2ll * a)
        {
            hi = mid;
        }
        if(sm < a)
            lo = mid;
    }
    intt sm = 0;
    forr(i , lo - k +1 , lo)
    {
        sm+=get(i , x);
    }
    if(a <= sm && sm <= 2ll * a)
    {
        forr(i , lo - k +1 , lo)
            ans.pb(i);
        answer(ans);
        return ;
    }
//    sm = 0;
//    forr(i , hi - k +1 , hi)
//    {
//        sm+=get(i , x);
//    }
//    if(a <= sm && sm <= 2ll * a)
//    {
//        forr(i , hi - k +1 , hi)
//            ans.pb(i);
//        answer(ans);
//        return ;
//    }
    impossible();
}

• Subtask 1: 5 / 5
• Subtask 2: 15 / 15
• Subtask 3: 10 / 10
• Subtask 4: 15 / 15
• Subtask 5: 15 / 15
• Subtask 6: 0 / 20
• Subtask 7: 0 / 20