Submission #1183502

#	Time	Username	Problem	Language	Result	Execution time	Memory
1183502		dion324	Dreaming (IOI13_dreaming)	C++20	100 / 100	91 ms	47844 KiB

dreaming

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

const int MAXN = 1e6 + 5;
vector<vector<pair<int, int>>> adj(MAXN);
vector<int> parent(MAXN, -1);
vector<int> dist(MAXN, 0);
vector<int> color(MAXN, 0);
int max_dist = 0;
int end_node = 0;

void dfs(int u, int c) {
    color[u] = c;
    if (dist[u] > max_dist) {
        max_dist = dist[u];
        end_node = u;
    }
    for (auto [v, w] : adj[u]) {
        if (color[v] != c) {
            parent[v] = u;
            dist[v] = dist[u] + w;
            dfs(v, c);
        }
    }
}

int travelTime(int N, int M, int L, int A[], int B[], int T[]) {
    if (N == 1) return 0;

    // Build adjacency list
    for (int i = 0; i < M; i++) {
        adj[A[i]].emplace_back(B[i], T[i]);
        adj[B[i]].emplace_back(A[i], T[i]);
    }

    vector<int> radii;
    int max_diameter = 0;
    int color_id = 1;

    for (int i = 0; i < N; i++) {
        if (!color[i]) {
            // First DFS to find one end of diameter
            max_dist = -1;
            dist[i] = 0;
            dfs(i, color_id);

            // Second DFS to find other end and diameter
            int start = end_node;
            max_dist = -1;
            parent[start] = -1;
            dist[start] = 0;
            dfs(start, color_id + 1);

            // Calculate diameter and radius
            int diameter = max_dist;
            max_diameter = max(max_diameter, diameter);

            // Find radius by finding minimal maximum distance
            int radius = diameter;
            for (int u = end_node; u != -1; u = parent[u]) {
                radius = min(radius, max(dist[u], diameter - dist[u]));
            }
            radii.push_back(radius);
            color_id += 2;
        }
    }

    sort(radii.rbegin(), radii.rend());

    if (radii.size() == 1) {
        return max_diameter;
    }
    if (radii.size() == 2) {
        return max(max_diameter, radii[0] + radii[1] + L);
    }
    return max({max_diameter, radii[0] + radii[1] + L, radii[1] + radii[2] + 2 * L});
}

• Subtask 1: 14 / 14
• Subtask 2: 10 / 10
• Subtask 3: 23 / 23
• Subtask 4: 18 / 18
• Subtask 5: 12 / 12
• Subtask 6: 23 / 23