Submission #679230

#	Time	Username	Problem	Language	Result	Execution time	Memory
679230		bebra	Boat (APIO16_boat)	C++17	9 / 100	2072 ms	18796 KiB

boat

#define _GLIBCXX_DEBUG_PEDANTIC
#include <bits/stdc++.h>
using namespace std;

#define dbg(x) cerr << #x << ": " << x << endl;


struct Seg {
    int l;
    int r;

    Seg(int _l = -1, int _r = -1) : l(_l), r(_r) {}


    bool empty() const {
        return r - l + 1 <= 0;
    }

    bool operator<(const Seg& other) const {
        return tie(l, r) < tie(other.l, other.r);
    }

    bool operator==(const Seg& other) const {
        return tie(l, r) == tie(other.l, other.r);
    }

    friend Seg intersect(const Seg& lhs, const Seg& rhs) {
        return {max(lhs.l, rhs.l), min(lhs.r, rhs.r)};
    }
};


const int MOD = 1e9 + 7;
const int INV2 = 500000004;

int add(int a, int b) {
    int res = a + b;
    if (res >= MOD) res -= MOD;
    return res;
}

int mul(long long a, int b) {
    return a * b % MOD;
}

const int MAX_N = 500 + 1;
Seg segs[MAX_N];
int dp[MAX_N][MAX_N * MAX_N];
int main_idx[MAX_N];


int main() {
    ios_base::sync_with_stdio(false);
    cin.tie(nullptr);
    int n;
    cin >> n;
    for (int i = 1; i <= n; ++i) {
        cin >> segs[i].l >> segs[i].r;
    }
    
    vector<Seg> states;
    for (int i = 1; i <= n; ++i) {
        for (int j = 1; j <= n; ++j) {
            if (segs[i].l <= segs[j].r) {
                states.emplace_back(segs[i].l, segs[j].r);
            }
            if (segs[i].l <= segs[j].l - 1) {
                states.emplace_back(segs[i].l, segs[j].l - 1);
            }
        }
    }
    sort(states.begin(), states.end());
    states.resize(unique(states.begin(), states.end()) - states.begin());
    int m = states.size();

    segs[0] = {-1, -1};
    dp[0][0] = 1;
    int ans = 0;
    for (int i = 1; i <= n; ++i) {
        main_idx[i] = lower_bound(states.begin(), states.end(), segs[i]) - states.begin();

        for (int j = 0; j < m; ++j) {
            auto [l1, r1] = states[j];
            if (segs[i].l > l1 || r1 > segs[i].r) continue;
            for (int k = 0; k < i; ++k) {
                auto [l2, r2] = segs[k];
                if (r1 < l2) {
                    continue;
                }
                if (r2 < l1) {
                    dp[i][j] = add(dp[i][j], mul(dp[k][main_idx[k]], r1 - l1 + 1));
                    continue;
                }
                auto [l3, r3] = intersect(states[j], segs[k]);

                dp[i][j] = add(dp[i][j], mul(dp[k][main_idx[k]], r1 - r3));

                int idx1 = lower_bound(states.begin(), states.end(), Seg{l3, r3}) - states.begin();
                dp[i][j] = add(dp[i][j], mul(dp[k][idx1], mul(r3 - l3, INV2)));

                if (l3 - 1 >= l2) {
                    int idx2 = lower_bound(states.begin(), states.end(), Seg{l2, l3 - 1}) - states.begin();
                    dp[i][j] = add(dp[i][j], mul(r3 - l1 + 1, dp[k][idx2]));
                }
            }
        }

        ans = add(ans, dp[i][main_idx[i]]);
    }
    cout << ans << '\n';
    return 0;
}

• Subtask 1: 9 / 9
• Subtask 2: 0 / 22
• Subtask 3: 0 / 27
• Subtask 4: 0 / 42