Submission #1037701

#	Time	Username	Problem	Language	Result	Execution time	Memory
1037701		thinknoexit	Thousands Islands (IOI22_islands)	C++17	1.75 / 100	24 ms	8292 KiB

islands

#include "islands.h"
#include <bits/stdc++.h>
using namespace std;
using ll = long long;
const int N = 1010;
vector<int> adj[N];
vector<int> cycle, path;
bool c[N], reach[N], vis[N];
int boat[N][N], bp, ava, n;
void dfs_sz(int v) {
    reach[v] = 1;
    for (auto& x : adj[v]) {
        if (!reach[x]) dfs_sz(x);
    }
}
bool dfs(int v, int p = -1) {
    if (vis[v]) {
        bp = v, ava = 1;
        return true;
    }
    vis[v] = 1;
    for (auto& x : adj[v]) {
        if (x == p) continue;
        if (dfs(x, v)) {
            if (ava) cycle.push_back(v), c[v] = 1;
            if (v == bp) ava = 0;
            return true;
        }
    }
    return false;
}
bool dfs2(int v, int p = -1) {
    if (c[v]) {
        path.push_back(v);
        return true;
    }
    vis[v] = 1;
    for (auto& x : adj[v]) {
        if (x == p) continue;
        if (!vis[x] && dfs2(x, v)) {
            path.push_back(v);
            return true;
        }
    }
    return false;
}
variant<bool, vector<int>> find_journey(int _N, int M, vector<int> U, vector<int> V) {
    n = _N;
    bool ch = 0;
    for (int i = 0;i < M;i++) {
        adj[U[i]].push_back(V[i]);
    }
    dfs_sz(0);
    memset(boat, -1, sizeof boat);
    for (int i = 0;i < M;i++) {
        if (!reach[U[i]]) continue;
        if (boat[U[i]][V[i]] == -1) {
            boat[U[i]][V[i]] = i;
        }
        else if (!ch) {
            ch = 1;
            cycle.push_back(U[i]), cycle.push_back(V[i]), c[U[i]] = c[V[i]] = 1;
        }
    }
    if (!ch && !dfs(0)) return false;
    return true;
    // find path to cycle
    memset(vis, 0, sizeof vis);
    dfs2(0);
    // path -> cycle -> elcyc -> htap
    vector<int> ans;
    {
        int sz = path.size();
        for (int i = 1;i < sz;i++) {
            ans.push_back(boat[path[i - 1]][path[i]]);
        }
    }
    {
        vector<int> cycle2;
        int last = path.back();
        int sz = cycle.size();
        for (int i = 0;i < sz;i++) {
            if (cycle[i] == last) {
                for (int j = 0;j < sz;j++) {
                    cycle2.push_back(cycle[(i + j) % sz]);
                }
                break;
            }
        }
        cycle = cycle2;
    }
    int sz = cycle.size();
    for (int i = 0;i < sz;i++) {
        ans.push_back(boat[cycle[i]][cycle[(i + 1) % sz]]);
    }
    for (int i = sz - 1;i >= 0;i--) {
        ans.push_back(boat[cycle[(i + 1) % sz]][cycle[i]]);
    }
    for (int i = 0;i < sz;i++) {
        ans.push_back(boat[cycle[(i + 1) % sz]][cycle[i]]);
    }
    for (int i = sz - 1;i >= 0;i++) {
        ans.push_back(boat[cycle[i]][cycle[(i + 1) % sz]]);
    }
    {
        int sz = path.size();
        for (int i = sz - 1;i >= 1;i--) {
            ans.push_back(boat[path[i - 1]][path[i]]);
        }
    }
    return ans;
}

• Subtask 1: 0 / 5
• Subtask 2: 1.75 / 5
• Subtask 3: 0 / 21
• Subtask 4: 0 / 24
• Subtask 5: 0 / 45