Submission #1077167

#	Time	Username	Problem	Language	Result	Execution time	Memory
1077167		Evirir	Railway Trip (JOI17_railway_trip)	C++17	20 / 100	2056 ms	8912 KiB

railway_trip

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

#define sz(x) (int)(x).size()
#define all(x) begin(x), end(x)
#define forn(i,a,b) for(int i=(a);i<(b);i++)
#define fore(i,a,b) for(int i=(a);i<=(b);i++)
#define pb push_back
#define F first
#define S second
using ll = long long;
using ii = pair<ll, ll>;

static constexpr int INF = 1e9;

int n,K,Q;
vector<int> a, lnxt, rnxt;
vector<vector<int>> adj;

vector<int> getLeft()
{
    vector<int> res(n, -1);
    vector<int> s;

    forn(i,0,n)
    {
        while (!s.empty() && a[s.back()] < a[i]) s.pop_back();
        if (!s.empty())
        {
            res[i] = s.back();
            if (a[s.back()] == a[i]) s.pop_back();
        }
        s.pb(i);
    }
    return res;
}

int bfs(int s, int t)
{
    vector<int> dist(n, INF);
    queue<int> q;
    dist[s] = 0;
    q.push(s);
    while (!q.empty())
    {
        int u = q.front(); q.pop();
        for (const auto v : adj[u])
        {
            if (dist[v] < INF) continue;
            dist[v] = dist[u] + 1;
            q.push(v);
        }
    }
    assert(dist[t] != INF);
    return dist[t];
}

void connect(int u, int v)
{
    adj[u].pb(v);
    adj[v].pb(u);
}

int main()
{
    cin.tie(0)->sync_with_stdio(0);

    cin>>n>>K>>Q;
    a.resize(n); adj.resize(n);
    forn(i,0,n)
    {
        cin>>a[i];
        a[i]--;
    }

    lnxt = getLeft();
    reverse(all(a));
    rnxt = getLeft();
    reverse(all(rnxt));
    reverse(all(a));
    forn(i,0,n)
    {
        if (rnxt[i] != -1) rnxt[i] = n - 1 - rnxt[i];
    }
    forn(i,0,n)
    {
        if (lnxt[i] != -1) connect(i, lnxt[i]);
        if (rnxt[i] != -1) connect(i, rnxt[i]);
    }

    forn(z,0,Q)
    {
        int u,v; cin>>u>>v; u--; v--;
        cout << bfs(u, v) - 1 << '\n';
    }

    return 0;
}

• Subtask 1: 5 / 5
• Subtask 2: 15 / 15
• Subtask 3: 0 / 25
• Subtask 4: 0 / 55