Submission #1166372

#	Time	Username	Problem	Language	Result	Execution time	Memory
1166372		merciless_lassie	Commuter Pass (JOI18_commuter_pass)	C++20	0 / 100	313 ms	110156 KiB

commuter_pass

#include "bits/stdc++.h"
using namespace std;
#define int long long
const int N = 1e6 + 5;
#define II pair<int,int>
#define fi first
#define se second
int n, m;
int s, t, U, V;
int f[N], f2[N];
vector<II> adj[N], adj2[N];
map<II, bool> mp;

// Utility function to update minimum values
template<class X, class Y> bool mini(X& x, const Y y) {
    if (x > y) return x = y, 1;
    return 0;
}

// Dijkstra to find shortest paths from a node
void dijkstra(int node) {
    memset(f, 0x3f, sizeof f);
    priority_queue<II, vector<II>, greater<II>> q;
    q.push({0, node});
    f[node] = 0;
    while (!q.empty()) {
        II u = q.top(); q.pop();
        if (u.fi != f[u.se]) continue;
        for (II v : adj[u.se]) {
            if (mini(f[v.se], f[u.se] + v.fi)) {
                q.push({f[v.se], v.se});
                mp[{u.se, v.se}] = 1;
            }
            if (f[v.se] == f[u.se] + v.fi) {
                mp[{u.se, v.se}] = 1;
            }
        }
    }
}

// Second Dijkstra on modified graph (zero-cost edges for shortest path edges)
void dijkstra2(int node) {
    memset(f2, 0x3f, sizeof f2);
    priority_queue<II, vector<II>, greater<II>> q;
    q.push({0, node});
    f2[node] = 0;
    while (!q.empty()) {
        II u = q.top(); q.pop();
        if (u.fi != f2[u.se]) continue;
        for (II v : adj2[u.se]) {
            if (mini(f2[v.se], f2[u.se] + v.fi)) {
                q.push({f2[v.se], v.se});
            }
        }
    }
}

signed main() {
    ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0);
    if (fopen("_ab.inp", "r")) {
        freopen("_ab.inp", "r", stdin);
        freopen("_ab.out", "w", stdout);
    }

    cin >> n >> m; 
    cin >> s >> t >> U >> V;
    
    for (int i = 1; i <= m; i++) {
        int u, v, c; cin >> u >> v >> c;
        adj[u].push_back({c, v});
        adj[v].push_back({c, u});
    }

    // Step 1: Find shortest paths from S
    dijkstra(s);
    
    // Step 2: Construct adj2 for zero-cost edges on the shortest path
    for (int i = 1; i <= n; i++) {
        for (II j : adj[i]) {
            if (mp[{i, j.se}]) {
                adj2[i].push_back({0, j.se});
            } else {
                adj2[i].push_back(j);
            }
        }
    }

    // Step 3: Find shortest paths from U using modified graph
    dijkstra2(U);
    
    cout << f2[V] << '\n';
    return 0;
}

Compilation message (stderr)

commuter_pass.cpp: In function 'int main()':
commuter_pass.cpp:61:16: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
   61 |         freopen("_ab.inp", "r", stdin);
      |         ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~
commuter_pass.cpp:62:16: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
   62 |         freopen("_ab.out", "w", stdout);
      |         ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~

• Subtask 1: 0 / 16
• Subtask 2: 0 / 15
• Subtask 3: 0 / 24
• Subtask 4: 0 / 45