Submission #1120218

#	Time	Username	Problem	Language	Result	Execution time	Memory
1120218		vjudge1	Event Hopping (BOI22_events)	C++17	0 / 100	335 ms	14016 KiB

events

#include <bits/stdc++.h>
using namespace std;
int n, q;
int s[100100];
int e[100100];
int p[100100];
int par[100100];
int nxt[100100][20];
int cmp(int i, int j) {
    return e[i] < e[j];
}
int get_par(int v) {
    if(par[v] == v) {
        return v;
    }
    return par[v] = get_par(par[v]);
}
int calc(int x, int y) {
    int ans = 0;
    for(int i = 17; i >= 0; i--) {
        int v = nxt[x][i];
        if(v > 0 && e[v] < e[y]) {
            ans += 1<<i;
            x = v;
        }
    }
    if(e[x] >= s[y]) {
        return ans;
    } else {
        return -1;
    }
}
int go(int x, int k) {
    for(int i = 17; i >= 0; i--) {
        int v = nxt[x][i];
        if(k >= (1<<i)) {
            k -= 1<<i;
            if(v == -1) return -1;
            x = v;
        }
    }
    return x;
}
int can(int x, int y, int k) {
    int v = get_par(x);
    int cnt = 0;
    int c = nxt[v][0];
    if(v == x || s[c] <= e[x]) {
        cnt++;
        x = c;
    }
    if(k - cnt - 1 <= 0) {
        return 0;
    }
    int t = go(x, k - cnt - 1);
    if(t == -1) {
        return 0;
    }
    if(e[t] >= s[y]) return 1;
    return 0;
}
void solve() {
    cin >> n >> q;
    for (int i = 1; i <= n; i++) {
        cin >> s[i] >> e[i];
        p[i] = i;
    }
    sort(p+1, p + n + 1, cmp);
    vector<int> st;
    for(int i = 1; i <= n; i++) {
        int j = p[i];
        while(st.size() > 0 && s[st.back()] >= s[j]) {
            par[st.back()] = j;
            st.pop_back();
        }
        if(st.size() > 0 && e[st.back()] == e[j] && s[st.back()] < s[j]) {
            par[j] = st.back();
        } else {
            par[j] = j;
            st.push_back(j);
        }
    }
    for(int i = 0; i < st.size(); i++) {
        if(i + 1 == st.size()) {
            nxt[st[i]][0] = -1;
        } else {
            if(e[st[i]] >= s[st[i+1]]) {
                nxt[st[i]][0] = st[i + 1];
            }
            else {
                nxt[st[i]][0] = -1;
            }
        }
    }
    for(int i = 1; i <= n; i++) {
        if(par[i] != i) {
            nxt[i][0] = get_par(i);
        }
    }
    for(int k = 1; k < 18; k++) {
        for(int i = 1; i <= n; i++) {
            int v = nxt[i][k-1];
            if(v != -1) {
                nxt[i][k] = nxt[v][k-1];
            } else {
                nxt[i][k] = -1;
            }
        }
    }
    for(int i = 1; i <= q; i++) {
        int x, y;
        cin >> x >> y;
        if(e[x] > e[y]) {
            swap(x, y);
        }
        if(e[x] >= s[y]) {
            cout << 0 << "\n";
        } else if(get_par(x) == get_par(y)){
            cout << 1 << "\n";
        } else {
            int k = calc(get_par(x), get_par(y));
            if(k == -1) {
                cout << "impossible\n";
            } else {
                if(can(x, y, k)) {
                    cout << k << "\n";
                } else if(can(x, y, k+1)) {
                    cout << k + 1 << "\n";
                } else {
                    cout << k + 2 << "\n";
                }
            }
        }
    }

}
int main() {
    solve();
}

Compilation message (stderr)

events.cpp: In function 'void solve()':
events.cpp:83:22: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   83 |     for(int i = 0; i < st.size(); i++) {
      |                    ~~^~~~~~~~~~~
events.cpp:84:18: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   84 |         if(i + 1 == st.size()) {
      |            ~~~~~~^~~~~~~~~~~~

• Subtask 1: 0 / 10
• Subtask 2: 0 / 10
• Subtask 3: 0 / 15
• Subtask 4: 0 / 15
• Subtask 5: 0 / 20
• Subtask 6: 0 / 30