Submission #600069

#	Time	Username	Problem	Language	Result	Execution time	Memory
600069		Valaki2	Fountain Parks (IOI21_parks)	C++17	35 / 100	1119 ms	155072 KiB

parks

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

#define x X
#define y Y

#define pb push_back
#define mp make_pair
#define pii pair<int, int>
#define fi first
#define se second

const int maxn = 2e5;
const vector<pii > directions = {mp(-2, 0), mp(0, -2), mp(0, 2), mp(2, 0)};

bool check_possibility(int n, vector<int> x, vector<int> y) {
    unordered_map<int, unordered_map<int, bool> > m;
    unordered_map<int, unordered_map<int, int> > f;
    for(int i = 0; i < n; i++) {
        f[x[i]][y[i]] = i + 1;
    }
    queue<int> q;
    q.push(0);
    m[x[0]][y[0]] = true;
    int cnt = 0;
    while(!q.empty()) {
        int cur = q.front();
        q.pop();
        cnt++;
        for(pii dir : directions) {
            pii new_point = mp(x[cur] + dir.fi, y[cur] + dir.se);
            if(f[new_point.fi][new_point.se] && !m[new_point.fi][new_point.se]) {
                m[new_point.fi][new_point.se] = true;
                int new_id = f[new_point.fi][new_point.se] - 1;
                q.push(new_id);
            }
        }
    }
    return (cnt == n);
}

struct fountain {
    int x, y, id;
    fountain() : x(0), y(0), id(-1) {}
    fountain(int x_, int y_, int id_) :
        x(x_), y(y_), id(id_) {}
};

int n;
vector<fountain > points;
vector<int> x;
vector<int> y;
unordered_map<int, unordered_map<int, int> > fountain_at;

unordered_map<int, unordered_map<int, bool> > bench_at;
unordered_map<int, unordered_map<int, bool> > road_at;
vector<int> ans_u;
vector<int> ans_v;
vector<int> ans_a;
vector<int> ans_b;

void build_road_bench(int road_u, int road_v, pii bench_pos) {
    ans_u.pb(road_u);
    ans_v.pb(road_v);
    ans_a.pb(bench_pos.fi);
    ans_b.pb(bench_pos.se);
    bench_at[bench_pos.fi][bench_pos.se] = true;
    road_at[(points[road_u].x + points[road_v].x) / 2][(points[road_u].y + points[road_v].y) / 2] = true;
}

vector<pii> get_bench_locations_pii(pii a, pii b) {
    fountain f_a = fountain(a.fi, a.se, -1), f_b = fountain(b.fi, b.se, -1);
    if(f_a.x == f_b.x) {
        int new_y = (f_a.y + f_b.y) / 2;
        a = mp(f_a.x + 1, new_y), b = mp(f_a.x - 1, new_y);
    } else {
        int new_x = (f_a.x + f_b.x) / 2;
        a = mp(new_x, f_a.y + 1), b = mp(new_x, f_a.y - 1);
    }
    return {min(a, b), max(a, b)};
}

vector<pii> get_bench_locations(int a_idx, int b_idx) {
    fountain f_a = points[a_idx], f_b = points[b_idx];
    pii a, b;
    if(f_a.x == f_b.x) {
        int new_y = (f_a.y + f_b.y) / 2;
        a = mp(f_a.x + 1, new_y), b = mp(f_a.x - 1, new_y);
    } else {
        int new_x = (f_a.x + f_b.x) / 2;
        a = mp(new_x, f_a.y + 1), b = mp(new_x, f_a.y - 1);
    }
    return {min(a, b), max(a, b)};
}

int get_middle_of_intersection(int a_idx, int b_idx) {
    pii a = mp(points[a_idx].x, points[a_idx].y);
    pii b = mp(points[b_idx].x, points[b_idx].y);
    int cnt = 0;
    for(pii dir : directions) {
        pii nei = mp(a.fi + dir.fi, a.se + dir.se);
        if(fountain_at[nei.fi][nei.se]) {
            cnt++;
        }
    }
    if(cnt == 4) {
        return a_idx;
    }
    cnt = 0;
    for(pii dir : directions) {
        pii nei = mp(b.fi + dir.fi, b.se + dir.se);
        if(fountain_at[nei.fi][nei.se]) {
            cnt++;
        }
    }
    if(cnt == 4) {
        return b_idx;
    }
    return -1;
}

pii get_bench_when_in_intersection(int a_idx, int b_idx) {
    // a is the middle, b is a neighbour
    fountain a = points[a_idx], b = points[b_idx];
    if(b.x < a.x) {
        return mp(a.x - 1, a.y + 1);
    }
    if(b.y < a.y) {
        return mp(a.x - 1, a.y - 1);
    }
    if(b.y > a.y) {
        return mp(a.x + 1, a.y + 1);
    }
    if(b.x > a.x) {
        return mp(a.x + 1, a.y - 1);
    }
}

bool bad_bench(pii bench, pii a, pii b) {
    if(a > b) {
        swap(a, b);
    }
    vector<pii > v = {a, b};
    for(pii dir : directions) {
        pii other = mp(bench.fi + dir.fi, bench.se + dir.se);
        vector<pii> corners = get_bench_locations_pii(bench, other);
        if(corners != v) {
            if(fountain_at[corners[0].fi][corners[0].se] &&
                fountain_at[corners[1].fi][corners[1].se] &&
                bench_at[other.fi][other.se] &&
                !road_at[(bench.fi + other.fi) / 2][(bench.se + other.se) / 2]) {
                return true;
            }
        }
    }
    return false;
}

void solve() {
    unordered_map<int, unordered_map<int, bool> > vis;
    queue<int> q;
    q.push(0);
    vis[x[0]][y[0]] = true;
    while(!q.empty()) {
        int cur = q.front();
        q.pop();
        for(pii dir : directions) {
            pii new_point = mp(x[cur] + dir.fi, y[cur] + dir.se);
            if(fountain_at[new_point.fi][new_point.se] && !vis[new_point.fi][new_point.se]) {
                vis[new_point.fi][new_point.se] = true;
                int new_id = fountain_at[new_point.fi][new_point.se] - 1;
                q.push(new_id);
                int mid = get_middle_of_intersection(cur, new_id);
                if(mid != -1) {
                    build_road_bench(cur, new_id, get_bench_when_in_intersection(mid, cur ^ new_id ^ mid));
                } else {
                    vector<pii> benches = get_bench_locations(cur, new_id);
                    if(!bench_at[benches[0].fi][benches[0].se] && !bad_bench(benches[0], mp(points[cur].x, points[cur].y), mp(points[new_id].x, points[new_id].y))) {
                        build_road_bench(cur, new_id, benches[0]);
                    } else {
                        build_road_bench(cur, new_id, benches[1]);
                    }
                }
            }
        }
    }
    //
}

#undef x
#undef y
int construct_roads(vector<int> x, vector<int> y) {
    // edge case
    if (x.size() == 1) {
        build({}, {}, {}, {});
        return 1;
    }
    // sample solution
    /*vector<int> u, v, a, b;
    u.push_back(0);
    v.push_back(1);
    a.push_back(x[0]+1);
    b.push_back(y[0]-1);
    build(u, v, a, b);*/
    n = x.size();
    if(!check_possibility(n, x, y)) {
        return 0;
    }
    X = x;
    Y = y;
    points.assign(n, fountain());
    for(int i = 0; i < n; i++) {
        points[i] = fountain(x[i], y[i], i);
        fountain_at[x[i]][y[i]] = i + 1;
    }
    solve();
    // build solution
    build(ans_u, ans_v, ans_a, ans_b);
    return 1;
}

/*
5
4 4
4 6
6 4
4 2
2 4
*/

Compilation message (stderr)

parks.cpp: In function 'std::pair<int, int> get_bench_when_in_intersection(int, int)':
parks.cpp:138:1: warning: control reaches end of non-void function [-Wreturn-type]
  138 | }
      | ^

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