Submission #1092901

#	Time	Username	Problem	Language	Result	Execution time	Memory
1092901		raphaelp	Swapping Cities (APIO20_swap)	C++14	100 / 100	374 ms	62196 KiB

swap

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

class UnionFind
{
private:
    vector<int> p;

public:
    UnionFind(int x)
    {
        p.assign(x, 0);
        for (int i = 0; i < x; i++)
            p[i] = i;
    }
    int find(int x) { return (x == p[x]) ? x : p[x] = find(p[x]); }
    bool merge(int a, int b)
    {
        int x = find(a), y = find(b);
        if (x == y)
            return 0;
        p[x] = y;
        return 1;
    }
};
vector<vector<int>> lca, lca2, lca3;
vector<int> depth;

void dfs(int x, int p, vector<vector<pair<int, int>>> &AR, vector<int> &best, int prof)
{
    depth[x] = prof;
    lca[0][x] = p;
    for (int i = 0; i < AR[x].size(); i++)
    {
        if (AR[x][i].first == p)
            continue;
        lca3[0][AR[x][i].first] = AR[x][i].second;
        dfs(AR[x][i].first, x, AR, best, prof + 1);
        best[x] = min(best[x], max(best[AR[x][i].first], AR[x][i].second));
    }
}
void dfs2(int x, int p, vector<vector<pair<int, int>>> &AR, vector<int> &best)
{
    lca2[0][x] = min(best[x], best[p]);
    for (int i = 0; i < AR[x].size(); i++)
    {
        if (AR[x][i].first == p)
            continue;
        best[AR[x][i].first] = min(best[AR[x][i].first], max(best[x], AR[x][i].second));
        dfs2(AR[x][i].first, x, AR, best);
    }
}
void init(int N, int M, vector<int> U, vector<int> V, vector<int> W)
{
    vector<vector<int>> Tab;
    vector<vector<pair<int, int>>> AR2(N);
    for (int i = 0; i < M; i++)
    {
        Tab.push_back({W[i], U[i], V[i]});
        AR2[U[i]].push_back({W[i], V[i]});
        AR2[V[i]].push_back({W[i], U[i]});
    }
    for (int i = 0; i < N; i++)
        sort(AR2[i].begin(), AR2[i].end());
    sort(Tab.begin(), Tab.end());
    UnionFind UF(N);
    vector<vector<pair<int, int>>> AR(N);
    vector<int> best(N, 1000000010);
    for (int i = 0; i < M; i++)
    {
        if (UF.merge(Tab[i][1], Tab[i][2]))
        {
            AR[Tab[i][1]].push_back({Tab[i][2], Tab[i][0]});
            AR[Tab[i][2]].push_back({Tab[i][1], Tab[i][0]});
        }
        else
        {
            best[Tab[i][1]] = min(best[Tab[i][1]], Tab[i][0]);
            best[Tab[i][2]] = min(best[Tab[i][2]], Tab[i][0]);
        }
    }
    for (int i = 0; i < N; i++)
    {
        if (AR2[i].size() >= 3)
        {
            best[i] = min(best[i], max(AR2[i][0].first, max(AR2[i][1].first, AR2[i][2].first)));
        }
    }
    lca.assign(log2(N) + 1, vector<int>(N, 0));
    lca2.assign(log2(N) + 1, vector<int>(N, 0));
    lca3.assign(log2(N) + 1, vector<int>(N, 0));
    depth.assign(N, 0);
    dfs(0, 0, AR, best, 0);
    dfs2(0, 0, AR, best);
    for (int i = 1; i <= log2(N); i++)
    {
        for (int j = 0; j < N; j++)
        {
            lca[i][j] = lca[i - 1][lca[i - 1][j]];
            lca2[i][j] = min(lca2[i - 1][j], lca2[i - 1][lca[i - 1][j]]);
            lca3[i][j] = max(lca3[i - 1][j], lca3[i - 1][lca[i - 1][j]]);
        }
    }
}

int getMinimumFuelCapacity(int X, int Y)
{
    int a = X, b = Y, N = lca[0].size();
    int best = 1000000010;
    int cost = 0;
    if (depth[a] > depth[b])
        swap(a, b);
    for (int i = log2(N); i >= 0; i--)
    {
        if (depth[lca[i][b]] >= depth[a])
        {
            best = min(best, lca2[i][b]);
            cost = max(cost, lca3[i][b]);
            b = lca[i][b];
        }
    }
    if (a == b)
        return (max(best, cost) == 1000000010) ? -1 : max(best, cost);
    for (int i = log2(N); i >= 0; i--)
    {
        if (lca[i][a] != lca[i][b])
        {
            best = min(best, min(lca2[i][a], lca2[i][b]));
            cost = max(cost, max(lca3[i][a], lca3[i][b]));
            a = lca[i][a];
            b = lca[i][b];
        }
    }
    best = min(best, min(lca2[0][a], lca2[0][b]));
    cost = max(cost, max(lca3[0][a], lca3[0][b]));
    return (max(best, cost) == 1000000010) ? -1 : max(best, cost);
}

/*int main()
{
    int N, M;
    cin >> N >> M;
    vector<int> U(M), V(M), W(M);
    for (int i = 0; i < M; i++)
    {
        cin >> U[i] >> V[i] >> W[i];
    }
    init(N, M, U, V, W);
    int Q;
    cin >> Q;
    for (int i = 0; i < Q; i++)
    {
        int a, b;
        cin >> a >> b;
        cout << getMinimumFuelCapacity(a, b) << '\n';
    }
}*/

Compilation message (stderr)

swap.cpp: In function 'void dfs(int, int, std::vector<std::vector<std::pair<int, int> > >&, std::vector<int>&, int)':
swap.cpp:34:23: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<std::pair<int, int> >::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   34 |     for (int i = 0; i < AR[x].size(); i++)
      |                     ~~^~~~~~~~~~~~~~
swap.cpp: In function 'void dfs2(int, int, std::vector<std::vector<std::pair<int, int> > >&, std::vector<int>&)':
swap.cpp:46:23: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<std::pair<int, int> >::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   46 |     for (int i = 0; i < AR[x].size(); i++)
      |                     ~~^~~~~~~~~~~~~~

• Subtask 1: 6 / 6
• Subtask 2: 7 / 7
• Subtask 3: 17 / 17
• Subtask 4: 20 / 20
• Subtask 5: 23 / 23
• Subtask 6: 27 / 27