Submission #1105295

#	Time	Username	Problem	Language	Result	Execution time	Memory
1105295		ShadowShark	Cities (BOI16_cities)	C++17	0 / 100	21 ms	8528 KiB

cities

#include <bits/stdc++.h>
using namespace std;
#define plii pair<long long, pair<int, int>>

const int maxN = 1e4 + 5; const long long inf = 1e18;
int n, m, k, T, s[maxN], pos[maxN];
long long dis[1000][maxN];
pair<int, int> lt[1000][maxN], rt[1000][maxN];
vector<pair<int, int>> adj[maxN];
vector<int> save[maxN];

void dijkstra() {
    priority_queue<plii, vector<plii>, greater<plii>> pq;

    for (int i = 1; i <= k; i++) {
        pq.push({0, {s[i], (1 << (i - 1))}});
        dis[(1 << (i - 1))][s[i]] = 0;
    }

    while (pq.size() > 0) {
        auto [len, rnd] = pq.top(); pq.pop();
        int u = rnd.first, mask = rnd.second;

        if (dis[mask][u] != len) continue;

        for (auto it: adj[u]) {
            int v = it.first, w = it.second;
            for (auto sub: save[mask])
                if (dis[sub][v] > dis[sub ^ mask][v] + len + w) {
                    dis[sub][v] = dis[sub ^ mask][v] + len + w;
                    lt[sub][v] = {sub ^ mask, v}, rt[sub][v] = {mask, u};
                    pq.push({dis[sub][v], {v, sub}});
                }
        }
    }
}

struct tmp {
    int mask, u, v;
} order[3000005];
int step = 0;

void backtrack(int u, int mask) {
    if (lt[mask][u].first != 0) {
        if (lt[mask][u].second != u) order[++step] = {lt[mask][u].first, lt[mask][u].second, u};
        backtrack(lt[mask][u].second, lt[mask][u].first);
    }

    if (rt[mask][u].first != 0) {
        if (rt[mask][u].second != u) order[++step] = {rt[mask][u].first, rt[mask][u].second, u};
        backtrack(rt[mask][u].second, rt[mask][u].first);
    }
}

string convert(int mask) {
    string s = "";
    while (mask > 0) {
        s = s + char(mask % 2 + '0');
        mask = mask / 2;
    }
    while (s.size() < k) s += "0";
    return s;
}

int main() {
    ios::sync_with_stdio(0); cin.tie(0); cout.tie(0);

    cin >> n >> m >> k >> T;

    for (int i = 1; i <= k; i++) {
        cin >> s[i];
        pos[s[i]] = 1;
    }

    for (int i = 1; i <= m; i++) {
        int u, v, w;
        cin >> u >> v >> w;

        adj[u].push_back({v, w});
        adj[v].push_back({u, w});
    }

    for (int mask = 1; mask < (1 << k); mask++)
        for (int S = mask; S > 0; S = (mask & (S - 1))) {
            save[S].push_back(mask);
    }

    for (int i = 1; i <= n; i++) {
        dis[0][i] = 0;
        for (int mask = 1; mask < (1 << k); mask++)
            dis[mask][i] = inf;
    }

    dijkstra();

    cout << dis[(1 << k) - 1][T] << '\n';
    //backtrack(T, (1 << k) - 1);

    /*cout << step << '\n';
    for (int i = step; i >= 1; i--) {
        auto [mask, u, v] = order[i];
        cout << convert(mask) << ' ' << u << ' ' << v << '\n';
    }*/

    return 0;
}

Compilation message (stderr)

cities.cpp: In function 'std::string convert(int)':
cities.cpp:61:21: warning: comparison of integer expressions of different signedness: 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} and 'int' [-Wsign-compare]
   61 |     while (s.size() < k) s += "0";
      |            ~~~~~~~~~^~~

• Subtask 1: 0 / 22
• Subtask 2: 0 / 14
• Subtask 3: 0 / 15
• Subtask 4: 0 / 23
• Subtask 5: 0 / 26