Submission #702451

#	Time	Username	Problem	Language	Result	Execution time	Memory
702451		GusterGoose27	City Mapping (NOI18_citymapping)	C++11	65.12 / 100	3 ms	596 KiB

citymapping

// #include "citymapping.h"

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

typedef long long ll;
typedef pair<int, int> pii;
typedef pair<ll, int> pli;

const int MAXN = 1000;
int t = 0;
mt19937 rng(6);
ll dist[2][MAXN];

class bucket {
public:
	vector<int> elems;
	int path_elem;
	int min_elem;
	ll mn_dist;
	bool m;
	bucket() {}
	bucket(int path, bool mn = 1) {
		min_elem = -1;
		path_elem = path;
		m = mn;
		mn_dist = 0;
	}
	void add(int i, ll d) {
		if (m && (min_elem == -1 || mn_dist > d)) {
			min_elem = i;
			mn_dist = d;
		}
		elems.push_back(i);
	}
};

void make_ans(vector<int> &vals, int a[], int b[], int w[], int f = -1) {
	if (vals.size() < 2) return;
	if (vals.size() == 2) {
		a[t] = vals[0];
		b[t] = vals[1];
		w[t] = get_distance(vals[0], vals[1]);
		t++;
		return;
	}
	int n = vals.size();
	if (f == -1) f = rng()%n;
	else {
		for (int i = 0; i < vals.size(); i++) {
			if (vals[i] == f) {
				f = i;
				break;
			}
		}
	}
	int mx = -1;
	for (int i = 0; i < n; i++) {
		if (i == f) continue;
		dist[0][i] = get_distance(vals[i], vals[f]);
		if (mx == -1 || dist[0][i] > dist[0][mx]) mx = i;
	}
	// int mx = f;
	// while (mx == f) mx = rng()%n;
	dist[0][f] = 0;
	for (int i = 0; i < n; i++) {
		if (i == f || i == mx) continue;
		dist[1][i] = get_distance(vals[i], vals[mx]);
	}
	dist[1][mx] = 0;
	dist[1][f] = dist[0][mx];
	vector<pli> path;
	map<ll, bucket> buckets;
	for (int i = 0; i < n; i++) {
		if (dist[0][i]+dist[1][i] == dist[0][mx]) {
			path.push_back(pli(dist[0][i], i));
			buckets[dist[1][i]-dist[0][i]] = bucket(i, (i != f && i != mx));
		}
	}
	sort(path.begin(), path.end());
	for (int i = 0; i < path.size()-1; i++) {
		a[t] = vals[path[i].second];
		b[t] = vals[path[i+1].second];
		w[t] = dist[0][path[i+1].second]-dist[0][path[i].second];
		t++;
	}
	for (int i = 0; i < n; i++) {
		if (dist[0][i]+dist[1][i] != dist[0][mx] || i == mx || i == f)
			buckets[dist[1][i]-dist[0][i]].add(vals[i], dist[0][i]);
	}
	for (auto it: buckets) {
		bucket bu = it.second;
		if (bu.m && bu.min_elem != -1) {
			a[t] = vals[bu.path_elem];
			b[t] = bu.min_elem;
			w[t] = bu.mn_dist-dist[0][bu.path_elem];
			// assert(bu.mn_dist > 0);
			assert(w[t] >= 0);
			t++;
		}
	}
	for (auto it: buckets) {
		if (it.second.m) make_ans(it.second.elems, a, b, w, it.second.min_elem);
		else make_ans(it.second.elems, a, b, w);
	}
}

void find_roads(int n, int q, int a[], int b[], int w[]) {
	vector<int> v(n);
	iota(v.begin(), v.end(), 1);
	make_ans(v, a, b, w);
	assert(t == n-1);
	// for (int i = 0; i < t; i++) assert(w[t] >= 0);
	return;
}

Compilation message (stderr)

citymapping.cpp: In function 'void make_ans(std::vector<int>&, int*, int*, int*, int)':
citymapping.cpp:51:21: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   51 |   for (int i = 0; i < vals.size(); i++) {
      |                   ~~^~~~~~~~~~~~~
citymapping.cpp:82:20: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<std::pair<long long int, int> >::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   82 |  for (int i = 0; i < path.size()-1; i++) {
      |                  ~~^~~~~~~~~~~~~~~

• Subtask 1: 9 / 9
• Subtask 2: 16 / 16
• Subtask 3: 13 / 13
• Subtask 4: 19 / 19
• Subtask 5: 8.12 / 43