Submission #864250

#	Time	Username	Problem	Language	Result	Execution time	Memory
864250		danikoynov	Event Hopping (BOI22_events)	C++14	25 / 100	1582 ms	9960 KiB

events

#include<bits/stdc++.h>

using namespace std;

const int maxn = 1e5 + 10;
     
struct interval
{
    int s, e, idx;
}seg[maxn];
     
int n, q;   
pair < int, int > task[maxn];

void input()
{
    cin >> n >> q;
    for (int i = 1; i <= n; i ++)
    {
        cin >> seg[i].s >> seg[i].e;
        seg[i].idx = i;
    }
    for (int i = 1; i <= q; i ++)
    {
        cin >> task[i].first >> task[i].second;
    }
}


bool cmp_end(interval seg1, interval seg2)
{
    
    return seg1.e < seg2.e;
}

int lf[maxn], rev[maxn], rf[maxn];
map < int, int > fix;
void build_graph()
{
    sort(seg + 1, seg + n + 1, cmp_end);
    for (int i = 1; i <= n; i ++)
    {
        rev[seg[i].idx] = i;
    }

    for (int i = 1; i <= n; i ++)
    {
        int l = 1;
        int r = i;
        while(l <= r)
        {
            int m = (l + r) / 2;
            if (seg[m].e < seg[i].s)
                l = m + 1;
            else
                r = m - 1;
        }
        lf[i] = l;
        //while(seg[lf[i]].e < seg[i].s)
           // lf[i] ++;


        if (fix[seg[i].e] == 0)
            fix[seg[i].e] = lf[i];
        else
            fix[seg[i].e] = min(fix[seg[i].e], lf[i]);
    }
}

void answer_queries()
{
    /**cout << "----------------------" << endl;
    for (int i = 1; i <= n; i ++)
        cout << seg[i].s << " :: " << seg[i].e << endl;*/
    
    for (int i = 1; i <= q; i ++)
    {
        int st = rev[task[i].first], en = rev[task[i].second];

        if (seg[st].e == seg[en].e && st != en)
        {
            cout << 1 << endl;
            continue;
        }
        if (st > en)
        {
            cout << "impossible" << endl;
            continue;
        }
        int steps = 0, last_left = en + 1;
        int bound_left = en;
        bool done = false;
        while(!(st >= bound_left))
        {
            ///cout << last_left << " " << bound_left << endl;
            steps ++;
            int new_left = bound_left;
            for (int i = bound_left; i < last_left; i ++)
            {
                new_left = min(new_left, lf[i]);
            }
            ///cout << "here " << lf[en] << " " << fix[seg[en].e] << " " << seg[en].s << endl;
            if (steps == 2)
                new_left = min(new_left, fix[seg[en].e]);
            ///cout << new_bound << endl;
            if (new_left == bound_left && steps > 1)
            {
                done = true;
                break;
            }
            
            last_left = bound_left;
            bound_left = new_left;
        }

        if (done)
            cout << "impossible" << endl;
        else
            cout << steps << endl;
    }
}
void solve()
{  
    input();
    build_graph();
    answer_queries();
}

int main()
{   
    ///speed();
    solve();

    return 0;
}

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