Submission #932686

#	Time	Username	Problem	Language	Result	Execution time	Memory
932686		Programmer123	Fountain Parks (IOI21_parks)	C++17	55 / 100	3550 ms	131320 KiB

parks

#ifndef LOCAL
#pragma GCC optimize("Ofast")
#pragma GCC target("avx2,sse4.2")
#endif

#include <bits/stdc++.h>
#include "parks.h"

std::unordered_map<int, int> map[100001];
int N;
std::unordered_map<int, std::vector<int>> rely[100002];
std::vector<std::pair<int, int>> vld[200000];
std::pair<int, int> assigned[200000];
std::unordered_set<int> taken[100002];
time_t stop;
std::default_random_engine Rand(std::random_device{}());

bool shuffle = false;
bool Shuffle = false;

bool doomed(int x) {
    for (auto a: vld[x]) if (!taken[a.first / 2].count(a.second)) return false;
    return true;
}

bool cantake(std::pair<int, int> a, int n) {
    for (auto x: rely[a.first / 2][a.second]) if (x > n && doomed(x)) return false;
    return true;
}

#ifdef LOCAL
size_t called = 0;
#endif

bool backtrack(int n) {
#ifdef LOCAL
    called++;
#endif
    if (n == N - 1) return true;
    if (clock() > stop) return false;
//    if (Shuffle && vld[n].size() == 2 && Rand() % 2) {
//        std::swap(vld[n][0], vld[n][1]);
//    }
    for (auto a: vld[n]) {
        if (taken[a.first / 2].count(a.second)) continue;
        taken[a.first / 2].insert(a.second);
        if (!cantake(a, n)) {
            taken[a.first / 2].erase(a.second);
            continue;
        }
        if (backtrack(n + 1)) {
            assigned[n] = a;
            return true;
        }
        taken[a.first / 2].erase(a.second);
    }
    return false;
}

int construct_roads(std::vector<int> x, std::vector<int> y) {
    stop = clock() + 3.4 * CLOCKS_PER_SEC;
    N = (int) x.size();
    if (N == 1) {
        build({}, {}, {}, {});
        return 1;
    }
    int maxx = x[0];
    int minx = x[0];
    int maxy = y[0];
    int miny = y[0];
    for (int i = 0; i < N; ++i) {
        maxx = std::max(maxx, x[i]);
        minx = std::min(minx, x[i]);
        maxy = std::max(maxy, y[i]);
        miny = std::min(miny, y[i]);
    }
    for (int i = 0; i < N; ++i) {
        map[x[i] / 2][y[i]] = i;
    }
    while (true) {
        std::vector<int> u, v, a, b;
        bool seen[N];
        for (int i = 0; i < N; ++i) {
            seen[i] = false;
        }
        std::queue<int> bfs;
        int start = 0;
        if (shuffle) {
            for (int i = 0; i < N; ++i) {
                if (x[i] < x[start]) start = i;
                if (x[i] == x[start] && y[i] < y[start]) start = i;
            }
        }
        if (Shuffle) {
            start = Rand() % N;
        }
        bfs.push(start);
        seen[start] = true;
        auto add = [&](int x, int y, std::vector<int> &data) {
            if (x < 0 || x > 200000) return;
            if (map[x / 2].count(y)) data.push_back(map[x / 2][y]);
        };
        auto edges = [&](int x, int y) {
            std::vector<int> result;
            add(x, y + 2, result);
            add(x, y - 2, result);
            add(x + 2, y, result);
            add(x - 2, y, result);
            if (Shuffle) {
                std::shuffle(result.begin(), result.end(), Rand);
            }
            return result;
        };
        int rem = N - 1;
        while (!bfs.empty()) {
            auto next = bfs.front();
            bfs.pop();
            for (auto n: edges(x[next], y[next])) {
                if (!seen[n]) {
                    seen[n] = true;
                    bfs.push(n);
                    rem--;
                    u.push_back(next);
                    v.push_back(n);
                }
            }
        }
        if (rem)
            return 0;

        std::function<std::vector<std::pair<int, int>>(int, int)> valid = [&x, &y, minx, maxx, miny, maxy](int u,
                                                                                                           int v) -> std::vector<std::pair<int, int>> {
            if (x[u] == x[v]) {
                int _y = (y[u] + y[v]) / 2;
                if (x[u] == minx) return {{minx - 1, _y}};
                if (x[u] == maxx) return {{maxx + 1, _y}};
                return {{x[u] + 1, _y},
                        {x[u] - 1, _y}};
            } else {
                int _x = (x[u] + x[v]) / 2;
                if (y[u] == miny) return {{_x, miny - 1}};
                if (y[u] == maxy) return {{_x, maxy + 1}};
                return {{_x, y[u] + 1},
                        {_x, y[u] - 1}};
            }
        };
        if (shuffle) {
            std::vector<std::pair<int, int>> Edges;
            for (int i = 0; i < N - 1; ++i) {
                Edges.emplace_back(u[i], v[i]);
            }
            std::sort(Edges.begin(), Edges.end(), [&](std::pair<int, int> a, std::pair<int, int> b) {
                int A = a.first;
                int B = b.first;
                if (x[A] == x[B]) return y[A] < y[B];
                return x[A] < x[B];
            });
            for (int i = 0; i < N - 1; ++i) {
                u[i] = Edges[i].first;
                v[i] = Edges[i].second;
            }
        }
        for (int i = 0; i < N - 1; ++i) {
            vld[i] = valid(u[i], v[i]);
            if (Shuffle && vld[i].size() == 2 && Rand() % 2) {
                std::swap(vld[i][0], vld[i][1]);
            }
        }
        for (int i = 0; i < N - 1; ++i) {
            for (auto n: vld[i]) {
                rely[n.first / 2][n.second].push_back(i);
            }
        }
        if (backtrack(0)) {
#ifdef LOCAL
            printf("Called backtrack %ld times.\n", called);
            called = 0;
#endif
            for (int i = 0; i < N - 1; ++i) {
                a.push_back(assigned[i].first);
                b.push_back(assigned[i].second);
            }
            build(u, v, a, b);
            return 1;
        }
#ifdef LOCAL
        printf("Called backtrack %ld times.\n", called);
        called = 0;
#endif
        for (auto _x: x) {
            rely[(_x - 1) / 2].clear();
            rely[(_x + 1) / 2].clear();
        }
        Shuffle = shuffle;
        shuffle = true;
        if (clock() > stop) return 0;
#ifdef LOCAL
        printf("Retrying...\n");
#endif
    }
    return 0;
}

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