Submission #1048455

#	Time	Username	Problem	Language	Result	Execution time	Memory
1048455		sofijavelkovska	Event Hopping (BOI22_events)	C++17	100 / 100	141 ms	16208 KiB

events

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

const int MAXN=(1<<18), LOG=17;

int l[MAXN], r[MAXN];
int tree[2*MAXN-1];

int compare(int x, int y)
{
    if (x==-1 || y==-1)
        return max(x, y);
    if (l[x]<l[y])
        return x;

    return y;
}

int find(int x, int l, int r, int lt, int rt)
{
    if (l>=rt || r<=lt)
        return -1;
    if (l>=lt && r<=rt)
        return tree[x];

    return compare(find(2*x+1, l, (l+r)/2, lt, rt), find(2*x+2, (l+r)/2, r, lt, rt));
}

void update(int x, int l, int r, int index, int value)
{
    if (l>index || r<=index)
        return;
    if (r-l==1)
    {
        tree[x]=compare(tree[x], value);
        return;
    }
    update(2*x+1, l, (l+r)/2, index, value);
    update(2*x+2, (l+r)/2, r, index, value);
    tree[x]=compare(tree[2*x+1], tree[2*x+2]);

    return;
}

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

    int n, q;
    cin >> n >> q;
    for (int i=0; i<n; i++)
        cin >> l[i] >> r[i];
    vector<int> temp;
    for (int i=0; i<n; i++)
    {
        temp.push_back(l[i]);
        temp.push_back(r[i]);
    }
    sort(temp.begin(), temp.end());
    vector<int> compress;
    for (auto x : temp)
        if (compress.empty() || x!=compress.back())
            compress.push_back(x);
    for (int i=0; i<2*MAXN-1; i++)
        tree[i]=-1;
    for (int i=0; i<n; i++)
    {
        int rightindex=lower_bound(compress.begin(), compress.end(), r[i])-compress.begin();
        update(0, 0, MAXN, rightindex, i);
    }
    int prev[n];
    for (int i=0; i<n; i++)
        prev[i]=-1;
    for (int i=0; i<n; i++)
    {
        int leftindex=lower_bound(compress.begin(), compress.end(), l[i])-compress.begin();
        int rightindex=lower_bound(compress.begin(), compress.end(), r[i])-compress.begin();
        prev[i]=find(0, 0, MAXN, leftindex, rightindex+1);
        if (prev[i]==i)
            prev[i]=-1;
    }
    int blift[n][LOG];
    for (int i=0; i<n; i++)
        for (int j=0; j<LOG; j++)
            blift[i][j]=-1;
    for (int i=0; i<n; i++)
        blift[i][0]=prev[i];
    for (int j=1; j<LOG; j++)
        for (int i=0; i<n; i++)
            if (blift[i][j-1]!=-1)
                blift[i][j]=blift[blift[i][j-1]][j-1];
    /*for (int j=0; j<3; j++)
    {
        for (int i=0; i<n; i++)
            cout << blift[i][j]+1 << ' ';
        cout << '\n';
    }*/
    while (q--)
    {
        int x, y;
        cin >> x >> y;
        x=x-1;
        y=y-1;
        if (x==y)
        {
            cout << 0 << '\n';
            continue;
        }
        if (r[x]>r[y])
        {
            cout << "impossible" << '\n';
            continue;
        }
        int total=0;
        //int i=lower_bound(compress.begin(), compress.end(), l[y])-compress.begin();
        //cout << "x y " << x+1 << ' ' << y+1 << '\n';
        //cout << "y " << y+1 << '\n';
        for (int j=LOG-1; j>=0; j--)
            if (blift[y][j]!=-1 && l[blift[y][j]]>r[x])
            {
                y=blift[y][j];
                //cout << "y " << y+1 << '\n';
                total=total+(1<<j);
            }
        if (l[y]<=r[x])
            cout << total+1 << '\n';
        else if (blift[y][0]!=-1 && l[blift[y][0]]<=r[x])
            cout << total+2 << '\n';
        else
            cout << "impossible" << '\n';
    }

    return 0;
}

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