Submission #685079

#	Time	Username	Problem	Language	Result	Execution time	Memory
685079		sharaelong	Fountain Parks (IOI21_parks)	C++17	100 / 100	678 ms	63504 KiB

parks

#include "parks.h"
#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef pair<int, int> pii;

struct DisjointSet {
    int n;
    vector<int> parent, rank;
    DisjointSet(int _n) : n(_n) {
        parent.resize(n);
        iota(parent.begin(), parent.end(), 0);
        rank.resize(n, 0);
    }

    int find(int u) {
        return parent[u] = (u == parent[u] ? u : find(parent[u]));
    }

    void merge(int u, int v) {
        u = find(u); v = find(v);
        if (u == v) return;
        if (rank[u] > rank[v]) swap(u, v);
        parent[u] = v;
        if (rank[u] == rank[v]) ++rank[v];
    }
};

int construct_roads(vector<int> x, vector<int> y) {
    int n = x.size();
    map<pii, int> fountains;
    for (int i=0; i<n; ++i) fountains[{ x[i], y[i] }] = i;
    set<pii> bench_cands;
    set<pii> road_cands; // store midpoint of adjacent fountains
    
    DisjointSet dsu(n);
    vector<vector<int>> points(200001);
    for (int i=0; i<n; ++i) points[x[i]].push_back(y[i]);
    for (auto& v: points) sort(v.begin(), v.end());
    for (int x=2; x<points.size(); x+=2) {
        for (int j=0; j<points[x].size(); ++j) {
            int y = points[x][j];
            if (fountains.count({ x-2, y })) {
                bench_cands.insert({ x-1, y-1 });
                bench_cands.insert({ x-1, y+1 });
                road_cands.insert({ x-1, y });
                dsu.merge(fountains[{ x-2, y }], fountains[{ x, y }]);
            }
            if (j+1 < points[x].size() && points[x][j+1] == y+2) {
                bench_cands.insert({ x-1, y+1 });
                bench_cands.insert({ x+1, y+1 });
                road_cands.insert({ x, y+1 });
                dsu.merge(fountains[{ x, y }], fountains[{ x, y+2 }]);
            }
        }
    }
    for (int i=1; i<n; ++i) {
        if (dsu.find(i) != dsu.find(0)) {
            return 0;
        }
    }

    vector<int> U, V, A, B;
    for (auto[a, b]: bench_cands) {
        bool is_black = ((a+b) % 4 == 2);
        if (is_black) {
            if (road_cands.count({ a, b+1 })) {
                U.push_back(fountains[{ a-1, b+1 }]);
                V.push_back(fountains[{ a+1, b+1 }]);
                A.push_back(a);
                B.push_back(b);
                road_cands.erase({ a, b+1 });
            } else if (road_cands.count({ a, b-1 })) {
                U.push_back(fountains[{ a-1, b-1 }]);
                V.push_back(fountains[{ a+1, b-1 }]);
                A.push_back(a);
                B.push_back(b);
                road_cands.erase({ a, b-1 });
            }
        } else {
            if (road_cands.count({ a-1, b })) {
                U.push_back(fountains[{ a-1, b-1 }]);
                V.push_back(fountains[{ a-1, b+1 }]);
                A.push_back(a);
                B.push_back(b);
                road_cands.erase({ a-1, b });
            } else if (road_cands.count({ a+1, b })) {
                U.push_back(fountains[{ a+1, b-1 }]);
                V.push_back(fountains[{ a+1, b+1 }]);
                A.push_back(a);
                B.push_back(b);
                road_cands.erase({ a+1, b });
            }   
        }
    }
    build(U, V, A, B);
    return 1;
}

Compilation message (stderr)

parks.cpp: In function 'int construct_roads(std::vector<int>, std::vector<int>)':
parks.cpp:40:20: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<std::vector<int> >::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   40 |     for (int x=2; x<points.size(); x+=2) {
      |                   ~^~~~~~~~~~~~~~
parks.cpp:41:24: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   41 |         for (int j=0; j<points[x].size(); ++j) {
      |                       ~^~~~~~~~~~~~~~~~~
parks.cpp:49:21: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   49 |             if (j+1 < points[x].size() && points[x][j+1] == y+2) {
      |                 ~~~~^~~~~~~~~~~~~~~~~~

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