Submission #1076769

#	Time	Username	Problem	Language	Result	Execution time	Memory
1076769		zsombor	Thousands Islands (IOI22_islands)	C++17	55 / 100	45 ms	12892 KiB

islands

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

int n, m, X = -1, Y = -1, I = -1;
vector<int> u;
vector<int> v;
vector<vector<int> > g(2e5);
vector<int> e(2e5, -1);
vector<int> oda;
vector<int> kor;
vector<bool> be(2e5, false);
vector<bool> ki(2e5, false);
vector<int> ans;

void solve1() {
    vector<int> a;
    vector<int> b;
    for (int i = 0; i < m; i++) {
        if (!u[i]) a.push_back(i);
        else b.push_back(i);
    }
    if (a.size() < 2 || b.size() < 1) return;
    ans = {a[0], b[0], a[1], a[0], b[0], a[1]};
}

void solve2() {
    ans.resize(12);
    for (int i = 0; i < m; i++) {
        if (u[i] == 0 && v[i] == 1) ans[0] = ans[8] = i;
        if (u[i] == 1 && v[i] == 0) ans[5] = ans[9] = i;
        if (u[i] == 0 && v[i] == 2) ans[3] = ans[11] = i;
        if (u[i] == 2 && v[i] == 0) ans[2] = ans[6] = i;
        if (u[i] == 1 && v[i] == 2) ans[1] = ans[7] = i;
        if (u[i] == 2 && v[i] == 1) ans[4] = ans[10] = i;
    }
}

void dfs3(int x) {
    if (I == -1 && g[x].size() >= 3) I = x;
    for (int i: g[x]) {
        if (i == (e[x] ^ 1)) continue;
        int y = v[i];
        if (e[y] > -1) continue;
        e[y] = i;
        dfs3(y);
    }
}

void solve3() {
    for (int i = 0; i < m; i++) g[u[i]].push_back(i);
    e[0] = m;
    dfs3(0);
    if (g[0].size() >= 2) I = 0;
    if (I == -1) return;
    X = I;
    while (X) {
        oda.push_back(e[X]);
        X = u[e[X]];
    }
    vector<int> z;
    for (int i: g[I]) if (i != (e[I] ^ 1)) z.push_back(i);
    kor = {z[0], z[0] ^ 1, z[1], z[1] ^ 1, z[0] ^ 1, z[0], z[1] ^ 1, z[1]};
    reverse(oda.begin(), oda.end());
    for (int i: oda) ans.push_back(i);
    for (int i: kor) ans.push_back(i);
    reverse(oda.begin(), oda.end());
    for (int i: oda) ans.push_back(i);
}

void dfs4(int x) {
    be[x] = true;
    for (int i: g[x]) {
        int y = v[i];
        if (be[y] && !ki[y]) {
            X = x;
            Y = y;
            I = i;
        }
        if (be[y]) continue;
        e[y] = i;
        dfs4(y);
    }
    ki[x] = true;
}

void solve4() {
    for (int i = 0; i < m; i += 2) g[u[i]].push_back(i);
    e[0] = m;
    dfs4(0);
    if (I == -1) return;
    kor.push_back(I);
    while (X != Y) {
        kor.push_back(e[X]);
        X = u[e[X]];
    }
    while (X) {
        oda.push_back(e[X]);
        X = u[e[X]];
    }
    reverse(oda.begin(), oda.end());
    for (int i: oda) ans.push_back(i);
    reverse(kor.begin(), kor.end());
    for (int i: kor) ans.push_back(i);
    for (int i: kor) ans.push_back(i ^ 1);
    reverse(kor.begin(), kor.end());
    for (int i: kor) ans.push_back(i);
    for (int i: kor) ans.push_back(i ^ 1);
    reverse(oda.begin(), oda.end());
    for (int i: oda) ans.push_back(i);
}

variant<bool, vector<int> > find_journey(int N, int M, vector<int> U, vector<int> V) {
    n = N;
    m = M;
    u = U;
    v = V;
    bool st3 = true, st4 = true;
    if (m % 2) st3 = st4 = false;
    for (int i = 0; i < m - 1; i += 2) {
        if (u[i] != v[i + 1]) st3 = false;
        if (v[i] != u[i + 1]) st3 = false;
        if (u[i] != u[i + 1]) st4 = false;
        if (v[i] != v[i + 1]) st4 = false;
    }
    if (n == 2) solve1();
    else if (st3) solve3();
    else if (st4) solve4();
    else solve2();
    if (ans.size()) return ans;
    return false;
}

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