Submission #805338

#	Time	Username	Problem	Language	Result	Execution time	Memory
805338		thimote75	Railway Trip (JOI17_railway_trip)	C++14	100 / 100	500 ms	27280 KiB

railway_trip

#include <bits/stdc++.h>

using namespace std;

using idata = vector<int>;
using igrid = vector<idata>;

template <typename A, typename B>
string to_string(pair<A, B> p) {
  return "(" + to_string(p.first) + ", " + to_string(p.second) + ")";
}
string to_string(string s) { return s; }
template <typename T> string to_string(T v) {
	bool first = true;
	string res = "[";
	for (const auto &x : v) {
		if (!first)
			res += ", ";
		first = false;
		res += to_string(x);
	}
	res += "]";
	return res;
}

void dbg_out() { cout << endl; }
template <typename Head, typename... Tail> void dbg_out(Head H, Tail... T) {
	cout << ' ' << to_string(H);
	dbg_out(T...);
}

#ifdef DEBUG
#define dbg(...) cout << "(" << #__VA_ARGS__ << "):", dbg_out(__VA_ARGS__)
#else
#define dbg(...)
#endif

struct Container {
    map<int, int> m;

    void insert(int height, int pos) {
        auto it = m.upper_bound(height);
        while (it != m.begin()) {
            it --;

            int h = (*it).first;
            m.erase(h);
            
            it = m.upper_bound(height);
        }

        m.insert({ height, pos });
    }

    int query (int height) {
        auto it = m.lower_bound(height);
        if (it == m.end()) return -1;

        return (*it).second;
    }
};

idata heights;

idata  left_road;
idata right_road;

igrid  left_road_2k;
igrid right_road_2k;

int N, K, Q;

const int MAXK = 20;

bool intersects (pair<int, int> a, pair<int, int> b) {
    if (b < a) swap (a, b);

    return a.second >= b.first;
}
pair<int, int> create (pair<int, int> start, int k) {
    int l = start.first;
    int r = start.second;

    int nl = min(
        left_road_2k[l][k],
        left_road_2k[r][k]
    );
    int nr = max(
        right_road_2k[l][k],
        right_road_2k[r][k]
    );

    return { nl, nr };
}

pair<pair<int, int>, int> jump_until (pair<int, int> start, pair<int, int> other) {
    int count = 0;
    for (int k = MAXK - 1; k >= 0; k --) {
        pair<int, int> potential = create(start, k);
        if (intersects(potential, other)) continue ;

        start = potential;
        count += 1 << k;
    }

    return { start, count };
}

void blf () {
    left_road_2k .resize(N, idata(MAXK, 0));
    right_road_2k.resize(N, idata(MAXK, N - 1));

    for (int i = 0; i < N; i ++) {
         left_road_2k[i][0] =  left_road[i];
        right_road_2k[i][0] = right_road[i];
    }

    for (int k = 0; k + 1 < MAXK; k ++) {
        for (int i = 0; i < N; i ++) {
            left_road_2k[i][k + 1] = min(
                left_road_2k[ left_road_2k[i][k]][k],
                left_road_2k[right_road_2k[i][k]][k]
            );
            right_road_2k[i][k + 1] = max(
                right_road_2k[ left_road_2k[i][k]][k],
                right_road_2k[right_road_2k[i][k]][k]
            );
        }
    }
}

idata bfs (int start) {
    queue<int> q; 
    idata answer(N, 1e9);
    answer[start] = 0;
    q.push(start);

    while (q.size() != 0) {
        int curr = q.front(); q.pop();

        for (int next : { left_road[curr], right_road[curr] }) {
            if (next == -1) continue ;

            if (answer[next] != 1e9) continue ;
            q.push(next);
            answer[next] = answer[curr] + 1;
        }
    }

    return answer;
}

int main () {
    cin >> N >> K >> Q;

    heights.resize(N);
    for (int i = 0; i < N; i ++) cin >> heights[i];

    left_road.resize(N, -1);
    Container cnt;
    for (int i = 0; i < N; i ++) {
        left_road[i] = cnt.query(heights[i]);
        if (i == 0) left_road[i] = 0;

        cnt.insert(heights[i], i);
    }

    cnt.m.clear();
    right_road.resize(N, -1);
    for (int i = N - 1; i >= 0; i --) {
        right_road[i] = cnt.query(heights[i]);
        if (i + 1 == N) right_road[i] = i;

        cnt.insert(heights[i], i);
    }

    blf();
    
    for (int q = 0; q < Q; q ++) {
        int a, b;
        cin >> a >> b;
        a --; b --;

        if (a > b) swap(a, b);

        const auto data1 = jump_until({ a, a }, { b, b });
        const auto data2 = jump_until({ b, b }, data1.first);
        
        cout << data1.second + data2.second << "\n";
    }
}

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