Submission #1020173

#	Time	Username	Problem	Language	Result	Execution time	Memory
1020173		bobbilyking	Longest Trip (IOI23_longesttrip)	C++17	5 / 100	913 ms	864 KiB

longesttrip

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

#define F(i, l, r) for (int i = (l); i < (r); ++i)
#define A(a) (a).begin(), (a).end()

int edge[300][300];
int parent[300];
int find(int i) {
    return i == parent[i] ? i : parent[i] = find(parent[i]);
}

int GN;

bool query(int A, int B) {
    assert(min(A, B) >= 0 and max(A, B) < GN);
    return edge[A][B] | edge[B][A];
}

void verify(vector<int> v) {
    set<int> cum(A(v));
    F(i, 1, v.size()) assert(query(v[i-1], v[i]));
    assert(v.size() == cum.size());
    for (auto x: v) assert(x >= 0 and x < GN);
}

vector<int> longest_trip(int N, int D)
{
    GN = N;
    // okay we're just going to build the spanning tree straight up, fuck this shit. 
    iota(parent, parent + N, 0ll);
    
    F(i, 0, N) F(j, i + 1, N) {
        if (are_connected({i}, {j})) {
            parent[find(i)] = find(j);
            edge[i][j] = edge[j][i] = 1;
        }
    }

    F(i, 0, N) if (find(i) != find(0)) {
        assert(D == 1);
        vector<int> v[2];
        F(j, 0, N) {
            v[find(j) == find(0)].push_back(j);
            assert(find(j) == find(i) || find(j) == find(0));
        }
        if (v[0].size() < v[1].size()) swap(v[0], v[1]);

        verify(v[0]);
        assert(v[0].size() >= v[1].size());

        return v[0];
    }

    vector<int> hamil;

    auto gen = [&]() {
        set<int> v;
        F(i, 0, N) if (find(A(hamil), i) == hamil.end()) v.insert(i);
        return v;
    };

    if (query({0}, {1})) {
        hamil = {0, 1};
    } else if (query({1}, {2})) {
        hamil = {1, 2};
    } else {
        hamil = {0, 2};
    }

    while (hamil.size() != N) { // this will reach N, with the exception of one case 
        // cout << "HOW " << endl;
        verify(hamil);

        if (query({hamil[0]}, {hamil.back()})) {
            // its true that we have a hamiltonian CYCLE, so any rotation is valid. 
            // (well in the case of n=2 behaves like it for our purposes)
        } else {
            // Pick any node not in hamil, this must be connected to either the front or the back.
            auto i = *gen().begin();
            if (query({hamil[0]}, {i})) hamil.insert(hamil.begin(), i);
            else {
                assert(query(hamil.back(), i));
                hamil.push_back(i);
            }
            
            continue;
        }

        // Okay, we want to find *any* connection between hamil and others, if exists already. 
        auto bad = gen();

        bool seen_edge = false;
        F(___, 0, hamil.size()) {
            auto v = hamil.back(); hamil.pop_back(); hamil.insert(hamil.begin(), v);
            verify(hamil);
            for (auto y: bad) if (edge[v][y]) {
                hamil.insert(hamil.begin(), y);
                verify(hamil);
                seen_edge = true; 
                goto end;
            }
        }
        end: 

        assert(seen_edge); // we already handle the CC = 2 case up there in this brute force approach
    }
    
    verify(hamil);
    assert(hamil.size() == N);

    return hamil;
}

Compilation message (stderr)

longesttrip.cpp: In function 'void verify(std::vector<int>)':
longesttrip.cpp:5:40: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
    5 | #define F(i, l, r) for (int i = (l); i < (r); ++i)
      |                                        ^
longesttrip.cpp:23:5: note: in expansion of macro 'F'
   23 |     F(i, 1, v.size()) assert(query(v[i-1], v[i]));
      |     ^
longesttrip.cpp: In function 'std::vector<int> longest_trip(int, int)':
longesttrip.cpp:72:25: warning: comparison of integer expressions of different signedness: 'std::vector<int>::size_type' {aka 'long unsigned int'} and 'int' [-Wsign-compare]
   72 |     while (hamil.size() != N) { // this will reach N, with the exception of one case
      |            ~~~~~~~~~~~~~^~~~
longesttrip.cpp:5:40: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
    5 | #define F(i, l, r) for (int i = (l); i < (r); ++i)
      |                                        ^
longesttrip.cpp:95:9: note: in expansion of macro 'F'
   95 |         F(___, 0, hamil.size()) {
      |         ^
In file included from /usr/include/c++/10/cassert:44,
                 from /usr/include/x86_64-linux-gnu/c++/10/bits/stdc++.h:33,
                 from longesttrip.cpp:3:
longesttrip.cpp:111:25: warning: comparison of integer expressions of different signedness: 'std::vector<int>::size_type' {aka 'long unsigned int'} and 'int' [-Wsign-compare]
  111 |     assert(hamil.size() == N);
      |            ~~~~~~~~~~~~~^~~~

• Subtask 0: 0 / 0
• Subtask 1: 5 / 5
• Subtask 2: 0 / 10
• Subtask 3: 0 / 25
• Subtask 4: 0 / 60