Submission #1079275

#	Time	Username	Problem	Language	Result	Execution time	Memory
1079275		boris_mihov	Skyscraper (JOI16_skyscraper)	C++17	100 / 100	817 ms	81124 KiB

skyscraper

#include <unordered_map>
#include <algorithm>
#include <iostream>
#include <numeric>
#include <cassert>
#include <vector>

typedef long long llong;
const int MAXN = 100 + 10;
const int MAXL = 1000 + 10;
const int MOD  = 1e9 + 7;

int n, l;
int a[MAXN];
int prefix[MAXN];
std::unordered_map <int,int> dp[MAXN][MAXN][2][2];

int f(int idx, int count, int sum, bool foundB, bool foundE)
{   
    if (idx + count - 2 > n || sum + 2 * (prefix[idx + count - 2] - prefix[idx - 1]) > l)
    {
        return 0;
    }

    if (idx == n + 1)
    {
        assert(count == 1 && sum <= l);
        return foundB && foundE;
    }

    if (dp[idx][count][foundB][foundE].count(sum))
    {
        return dp[idx][count][foundB][foundE][sum];
    }

    llong res = f(idx + 1, count + 1, sum - 2 * a[idx], foundB, foundE);
    if (!foundB)
    {
        res += f(idx + 1, count + 1, sum - a[idx], 1, foundE);
    }

    if (!foundE)
    {
        res += f(idx + 1, count + 1, sum - a[idx], foundB, 1);
    }

    if (count >= 1) 
    {
        res += (2LL * count - foundB - foundE) * f(idx + 1, count, sum, foundB, foundE);
        if (!foundB)
        {
            res += 1LL * (count - foundE) * f(idx + 1, count, sum + a[idx], 1, foundE);
            if (foundE && count == 1 && idx == n)
            {
                res += f(idx + 1, count, sum + a[idx], 1, foundE);
            }
        }

        if (!foundE)
        {
            res += 1LL * (count - foundB) * f(idx + 1, count, sum + a[idx], foundB, 1);
            if (foundB && count == 1 && idx == n)
            {
                res += f(idx + 1, count, sum + a[idx], foundB, 1);
            }
        }
    }

    if (count >= 2) 
    {
        int cntFree = count - foundB - foundE;
        res += 1LL * cntFree * (cntFree - 1) * f(idx + 1, count - 1, sum + 2 * a[idx], foundB, foundE);

        if (foundB)
        {
            res += 1LL * (count - 1 - foundE) * f(idx + 1, count - 1, sum + 2 * a[idx], foundB, foundE);
        }

        if (foundE)
        {
            res += 1LL * (count - 1 - foundB) * f(idx + 1, count - 1, sum + 2 * a[idx], foundB, foundE);
        }

        if (foundB && foundE && idx == n)
        {
            res += f(idx + 1, count - 1, sum + 2 * a[idx], foundB, foundE);
        }
    }

    return dp[idx][count][foundB][foundE][sum] = res % MOD;
}

void solve()
{
    if (n == 1)
    {
        std::cout << 1 << '\n';
        return;
    }

    std::sort(a + 1, a + 1 + n);
    for (int i = 1 ; i <= n ; ++i)
    {
        prefix[i] = prefix[i - 1] + a[i];
    }

    std::cout << f(1, 0, 0, 0, 0) << '\n';
}

void input()
{
    std::cin >> n >> l;
    for (int i = 1 ; i <= n ; ++i)
    {
        std::cin >> a[i];
    }
}

void fastIOI()
{
    std::ios_base:: sync_with_stdio(0);
    std::cout.tie(nullptr);
    std::cin.tie(nullptr);
}

int main()
{
    fastIOI();
    input();
    solve();

    return 0;
}

• Subtask 1: 5 / 5
• Subtask 2: 15 / 15
• Subtask 3: 80 / 80