Submission #1281496

#	Time	Username	Problem	Language	Result	Execution time	Memory
1281496		red_souls	Fire (BOI24_fire)	C++17	100 / 100	71 ms	28096 KiB

Main

#include <bits/stdc++.h>
#define ll long long
#define task "FIRE"
using namespace std;

const int N = 1e6 + 16;
const ll INF = 1e18;
int n, m;
ll s[N], e[N];

namespace sub6 {
    ll cnt, result = INF;
    pair <ll, ll> a[N];

    vector < pair <ll, ll> > checkLines;

    bool cmp(pair <ll, ll> A, pair <ll, ll> B) {
        if (A.first == B.first) return A.second > B.second;
        return A.first < B.first;
    }

    const int LG = 21; // 2^21 > 1e6
    static ll prefMax[N];
    static ll starts[N];
    static int up[LG][N];

    // tìm last index với starts[idx] <= x (trả về 0..n)
    inline int lastIndexLE(ll x, int n) {
        int l = 1, r = n, ans = 0;
        while (l <= r) {
            int mid = (l + r) >> 1;
            if (starts[mid] <= x) {
                ans = mid;
                l = mid + 1;
            } else r = mid - 1;
        }
        return ans;
    }

    void build(int n) {
        prefMax[0] = -INF;
        for (int i = 1; i <= n; ++i) {
            starts[i] = a[i].first;
            prefMax[i] = max(prefMax[i - 1], a[i].second);
        }
        // up[0][i] = last index with start <= prefMax[i] + 1
        for (int i = 1; i <= n; ++i) {
            int j = lastIndexLE(prefMax[i] + 1, n);
            if (j <= i) up[0][i] = 0; // không tiến được
            else up[0][i] = j;
        }
        for (int k = 1; k < LG; ++k) {
            for (int i = 1; i <= n; ++i) {
                int mid = up[k - 1][i];
                up[k][i] = (mid == 0) ? 0 : up[k - 1][mid];
            }
        }
    }

    // trả về số bước để cover [p, R] (tọa độ) hoặc -1
    ll query(pair<ll,ll> target, int n) {
        ll p = target.first, R = target.second;
        int idx = lastIndexLE(p, n);         // index các interval có start <= p
        if (idx == 0) return -1;
        if (prefMax[idx] < p) return -1;     // không thể bắt đầu phủ p
        if (prefMax[idx] >= R) return 1;     // 1 bước là đủ

        int cur = idx;
        int added = 0;
        for (int k = LG - 1; k >= 0; --k) {
            int to = up[k][cur];
            if (to != 0 && prefMax[to] < R) {
                cur = to;
                added += (1 << k);
            }
        }
        int nxt = up[0][cur];
        if (nxt == 0) return -1;
        added += 1;
        return 1 + added;
    }

    void solve() {
        checkLines.clear();
        checkLines.push_back({0, m - 1});
        for (int i = 1; i <= n; i++) {
            if (s[i] > e[i]) {
                checkLines.push_back({e[i], e[i] + m - 1});
                e[i] += m;
            }
            a[i] = {s[i], e[i] - 1};
        }
        sort(a + 1, a + 1 + n, cmp);
        build(n);
        for (auto x : checkLines) {
            ll ans = query(x, n);
            if (ans == -1) continue;
            result = min(result, ans);
        }
        if (result == INF) result = -1;
        cout << result;
    }
}

int main() {
    ios_base :: sync_with_stdio(false);
    cin.tie(0);
    cout.tie(0);

    if (fopen(task".inp", "r")) {
        freopen(task".inp", "r", stdin);
        freopen(task".out", "w", stdout);
    }

    cin >> n >> m;
    for (int i = 1; i <= n; i++) {
        cin >> s[i] >> e[i];
    }
    sub6 :: solve();

    return 0;
}

Compilation message (stderr)

Main.cpp: In function 'int main()':
Main.cpp:111:16: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
  111 |         freopen(task".inp", "r", stdin);
      |         ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~
Main.cpp:112:16: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
  112 |         freopen(task".out", "w", stdout);
      |         ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~

• Subtask 1: 14 / 14
• Subtask 2: 17 / 17
• Subtask 3: 9 / 9
• Subtask 4: 13 / 13
• Subtask 5: 21 / 21
• Subtask 6: 26 / 26