Submission #1067012

#	Time	Username	Problem	Language	Result	Execution time	Memory
1067012		j_vdd16	Thousands Islands (IOI22_islands)	C++17	1.75 / 100	28 ms	6688 KiB

islands

#include "islands.h"

#include <variant>
#include <algorithm>
#include <bitset>
#include <cstdint>
#include <cstring>
#include <iostream>
#include <limits.h>
#include <math.h>
#include <map>
#include <numeric>
#include <queue>
#include <set>
#include <stack>
#include <string>
#include <vector>

//#define int long long
#define loop(X, N) for(int X = 0; X < (N); X++)
#define all(V) V.begin(), V.end()
#define rall(V) V.rbegin(), V.rend()

using namespace std;

typedef vector<int> vi;
typedef vector<vi> vvi;
typedef pair<int, int> ii;
typedef vector<ii> vii;
typedef vector<vector<ii>> vvii;
typedef vector<bool> vb;
typedef vector<vector<bool>> vvb;

typedef uint64_t u64;
typedef int64_t i64;

int n, m;
vvi adj1, adj2;

vb vis;
vi depths;

int counter = 0;
vii inOut;
void dfs(int node, int d) {
    if (vis[node]) {
        return;
    }
    vis[node] = true;
    depths[node] = d;

    inOut[node].first = counter++;

    for (int child : adj1[node]) {
        dfs(node, d + 1);
    }

    inOut[node].second = counter++;
}

bool isAncestor(int a, int b) {
    return inOut[a].first <= inOut[b].first && inOut[b].first <= inOut[a].second;
}

bool success = false;
int isPossible(int node) {
    if (vis[node]) {
        return node;
    }
    vis[node] = true;

    int furthestBack = node;
    int cycleCount = 0;
    for (int child : adj1[node]) {
        int res = isPossible(child);
        if (isAncestor(res, node)) {
            cycleCount++;
            if (depths[res] < depths[furthestBack]) {
                furthestBack = res;
            }
        }
    }

    if (cycleCount >= 2) {
        success = true;
    }

    return furthestBack;
}

std::variant<bool, std::vector<int>> find_journey(int N, int M, vi U, vi V) {
    n = N;
    m = M;
    adj1 = vvi(n);
    adj2 = vvi(n);
    loop(i, m) {
        adj1[U[i]].push_back(V[i]);
        adj2[V[i]].push_back(U[i]);
    }

    vis = vb(n);
    depths = vi(n);
    counter = 0;
    inOut = vii(n);
    dfs(0, 0);
    vis = vb(n);

    success = false;
    isPossible(0);

    return success;
}

Compilation message (stderr)

islands.cpp: In function 'void dfs(int, int)':
islands.cpp:54:14: warning: unused variable 'child' [-Wunused-variable]
   54 |     for (int child : adj1[node]) {
      |              ^~~~~

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