Submission #1074192

#	Time	Username	Problem	Language	Result	Execution time	Memory
1074192		Zicrus	Thousands Islands (IOI22_islands)	C++17	3.50 / 100	34 ms	8652 KiB

islands

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

typedef long long ll;

int n, m;
vector<vector<pair<int, int>>> adj, revAdj; // edgeId, node
vector<bool> vst, edgeUsed;
stack<int> stk;
vector<int> lnk, sz, acc;
vector<int> numPaths;

void dfs1(int cur) {
    vst[cur] = true;
    for (auto &e : adj[cur]) {
        if (vst[e.second]) continue;
        dfs1(e.second);
    }
    stk.push(cur);
}

int dfs2(int cur, int rep) {
    vst[cur] = true;
    lnk[cur] = rep;
    sz[rep]++;
    int last = cur;
    for (auto &e : revAdj[cur]) {
        if (vst[e.second]) continue;
        edgeUsed[e.first] = true;
        last = dfs2(e.second, rep);
    }
    if (cur == rep && cur != last) {
        for (auto &e : adj[cur]) {
            if (e.second == last) {
                edgeUsed[e.first] = true;
                break;
            }
        }
    }
    return last;
}

int dfsPaths(int cur) {
    vst[cur] = true;
    int res = 0;
    for (auto &e : revAdj[cur]) {
        if (edgeUsed[e.first]) continue;
        if (vst[e.second]) {
            res += numPaths[e.second];
        }
        else {
            res += dfsPaths(e.second);
        }
    }
    return numPaths[cur] = res;
}

variant<bool, vector<int>> find_journey(int N, int M, vector<int> U, vector<int> V) {
    n = N; m = M;
    lnk = vector<int>(n);
    sz = vector<int>(n);
    acc = vector<int>(n);
    adj = vector<vector<pair<int, int>>>(n);
    revAdj = vector<vector<pair<int, int>>>(n);
    for (int i = 0; i < n; i++) lnk[i] = i;
    for (int i = 0; i < m; i++) {
        adj[U[i]].push_back({i, V[i]});
        revAdj[V[i]].push_back({i, U[i]});
    }
    edgeUsed = vector<bool>(m);
    vst = vector<bool>(n);
    for (int i = 0; i < n; i++) {
        if (vst[i]) continue;
        dfs1(i);
    }
    vst = vector<bool>(n);
    while (!stk.empty()) {
        ll cur = stk.top(); stk.pop();
        if (vst[cur]) continue;
        dfs2(cur, cur);
    }
    
    vst = vector<bool>(n);
    numPaths = vector<int>(n);
    vst[0] = true;
    numPaths[0] = 1;
    for (int i = 0; i < n; i++) {
        if (vst[i]) continue;
        dfsPaths(i);
    }

    vector<int> compPaths(n);
    vector<int> rep(n);
    int a = -1, b = -1;
    for (int i = 0; i < n; i++) {
        if (sz[lnk[i]] <= 1) continue;
        compPaths[lnk[i]] += numPaths[i];
        if (compPaths[lnk[i]] >= 2) {
            a = rep[lnk[i]];
            b = i;
            break;
        }
        rep[lnk[i]] = i;
    }

    return a != -1;
}

#ifdef TEST
#include "grader.cpp"
#endif

Compilation message (stderr)

islands.cpp: In function 'std::variant<bool, std::vector<int, std::allocator<int> > > find_journey(int, int, std::vector<int>, std::vector<int>)':
islands.cpp:95:17: warning: variable 'b' set but not used [-Wunused-but-set-variable]
   95 |     int a = -1, b = -1;
      |                 ^

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