Submission #1072024

#	Time	Username	Problem	Language	Result	Execution time	Memory
1072024		shmax	Fountain Parks (IOI21_parks)	C++17	55 / 100	3570 ms	116504 KiB

parks

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

using namespace std;
using i32 = int;
#define int long long
#define len(x) (int)(x.size())
template<typename T>
using vec = vector<T>;

struct DSU {
public:
    DSU() : _n(0) {}

    explicit DSU(int n) : _n(n), parent_or_size(n, -1) {}

    int unite(int a, int b) {
        assert(0 <= a && a < _n);
        assert(0 <= b && b < _n);
        int x = leader(a), y = leader(b);
        if (x == y) return x;
        if (-parent_or_size[x] < -parent_or_size[y]) std::swap(x, y);
        parent_or_size[x] += parent_or_size[y];
        parent_or_size[y] = x;
        return x;
    }

    bool one(int a, int b) {
        assert(0 <= a && a < _n);
        assert(0 <= b && b < _n);
        return leader(a) == leader(b);
    }

    int leader(int a) {
        assert(0 <= a && a < _n);
        if (parent_or_size[a] < 0) return a;
        return parent_or_size[a] = leader(parent_or_size[a]);
    }

    int size(int a) {
        assert(0 <= a && a < _n);
        return -parent_or_size[leader(a)];
    }

    std::vector<std::vector<int>> groups() {
        std::vector<int> leader_buf(_n), group_size(_n);
        for (int i = 0; i < _n; i++) {
            leader_buf[i] = leader(i);
            group_size[leader_buf[i]]++;
        }
        std::vector<std::vector<int>> result(_n);
        for (int i = 0; i < _n; i++) {
            result[i].reserve(group_size[i]);
        }
        for (int i = 0; i < _n; i++) {
            result[leader_buf[i]].push_back(i);
        }
        result.erase(
                std::remove_if(result.begin(), result.end(),
                               [&](const std::vector<int> &v) { return v.empty(); }),
                result.end());
        return result;
    }

private:
    int _n;
    // root node: -1 * component size
    // otherwise: parent
    std::vector<int> parent_or_size;
};


i32 construct_roads(std::vector<i32> _x, std::vector<i32> _y) {
    int n = len(_x);
    map<pair<int, int>, int> mp;
    for (int i = 0; i < n; i++) {
        mp[{_x[i], _y[i]}] = i;
    }

    for (int times = 0; times < 10; times++) {
        vec<pair<int, int>> edges;
        DSU dsu(n);
        for (int i = 0; i < n; i++) {
            vec<pair<int, int>> moves = {{-2, 0},
                                         {2,  0},
                                         {0,  -2},
                                         {0,  2}};
            for (auto [dx, dy]: moves) {
                int nx = _x[i] + dx;
                int ny = _y[i] + dy;
                if (!mp.count({nx, ny})) continue;
                edges.push_back({i, mp[{nx, ny}]});
            }
        }
        mt19937 rnd(chrono::steady_clock::now().time_since_epoch().count());
        shuffle(edges.begin(), edges.end(), rnd);

        vec<pair<int, int>> used_edges;
        for (auto [a, b]: edges) {
            if (dsu.one(a, b)) continue;
            dsu.unite(a, b);
            used_edges.emplace_back(a, b);
        }
        if (dsu.size(0) != n) continue;
        map<pair<int, int>, int> benches;
        map<int, pair<int, int>> benches_pos;
        int idx = 0;
        for (auto [a, b]: used_edges) {
            auto [x1, y1] = pair<int, int>{_x[a], _y[a]};
            auto [x2, y2] = pair<int, int>{_x[b], _y[b]};
            if (x1 == x2) {
                if (!benches.count({x1 - 1, (y1 + y2) / 2}))
                    benches[{x1 - 1, (y1 + y2) / 2}] = idx++, benches_pos[idx - 1] = {x1 - 1, (y1 + y2) / 2};
                if (!benches.count({x1 + 1, (y1 + y2) / 2}))
                    benches[{x1 + 1, (y1 + y2) / 2}] = idx++, benches_pos[idx - 1] = {x1 + 1, (y1 + y2) / 2};
            } else {
                if (!benches.count({(x1 + x2) / 2, y1 - 1}))
                    benches[{(x1 + x2) / 2, y1 - 1}] = idx++, benches_pos[idx - 1] = {(x1 + x2) / 2, y1 - 1};
                if (!benches.count({(x1 + x2) / 2, y1 + 1}))
                    benches[{(x1 + x2) / 2, y1 + 1}] = idx++, benches_pos[idx - 1] = {(x1 + x2) / 2, y1 + 1};
            }
        }
        vec<vec<int>> g(n - 1 + len(benches));
        int idt = 0;
        for (auto [a, b]: used_edges) {
            auto [x1, y1] = pair<int, int>{_x[a], _y[a]};
            auto [x2, y2] = pair<int, int>{_x[b], _y[b]};
            if (x1 == x2) {
                g[idt].push_back(n - 1 + benches[{x1 - 1, (y1 + y2) / 2}]);
                g[idt].push_back(n - 1 + benches[{x1 + 1, (y1 + y2) / 2}]);
            } else {
                g[idt].push_back(n - 1 + benches[{(x1 + x2) / 2, y1 - 1}]);
                g[idt].push_back(n - 1 + benches[{(x1 + x2) / 2, y1 + 1}]);
            }
            idt++;
        }

//        matching
//        shuffle
        for (int i = 0; i < n - 1; i++) {
            shuffle(g[i].begin(), g[i].end(), rnd);
        }
        vec<int> match(n - 1 + len(benches), -1);
        vec<bool> used(n - 1 + len(benches), false);
        function<bool(int)> dfs = [&](int v) -> bool {
            if (used[v]) return false;
            used[v] = true;
            for (auto u: g[v]) {
                if (match[u] == -1 || dfs(match[u])) {
                    match[u] = v;
                    match[v] = u;
                    return true;
                }
            }
            return false;
        };

        bool flag = true;
        do {
            flag = false;
            fill(used.begin(), used.end(), false);
            for (int i = 0; i < n - 1; i++) {
                if (match[i] == -1) {
                    if (dfs(i)) {
                        flag = true;
                    }
                }
            }
        } while (flag);

        int cnt = 0;
        for (int i = 0; i < n - 1; i++) {
            if (match[i] != -1) cnt++;
        }

        if (cnt == n - 1) {
            vec<i32> x_benches, y_benches;
            vec<i32> u, v;
            for (int i = 0; i < n - 1; i++) {
                x_benches.push_back(benches_pos[match[i]-n+1].first);
                y_benches.push_back(benches_pos[match[i]-n+1].second);
                u.push_back(used_edges[i].first);
                v.push_back(used_edges[i].second);
            }
            build(u, v, x_benches, y_benches);
            return 1;
        }


    }

    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