70 lines
1.8 KiB
C++
70 lines
1.8 KiB
C++
#include <bits/stdc++.h>
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#define INF 0x7FFFFFFF
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using namespace std;
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using ll = long long;
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using pll = pair<ll, ll>;
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using graph = vector<vector<pll>>;
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const int MAXN = 510;
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vector<ll> dijk(int x, graph& g) {
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priority_queue<pll> pq;
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pq.push({0, x});
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vector<ll> dist(MAXN, INF);
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while (pq.size()){
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auto [w, v] = pq.top();
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pq.pop();
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w = -w;
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if (dist[v] <= w) continue;
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dist[v] = w;
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for (auto [u, ww] : g[v]) {
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if (dist[u] <= w + ww) continue;
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pq.push({-(w+ww), u});
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}
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}
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return dist;
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}
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ll almost_dijk(int s, int d, graph& g, vector<ll>& dist_s, vector<ll>& dist_d) {
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ll best = dist_s[d];
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if (best == INF) return -1;
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priority_queue<pll> pq;
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pq.push({0, s});
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vector<ll> dist(MAXN, INF);
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while (pq.size()){
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auto [w, v] = pq.top();
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pq.pop();
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w = -w;
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if (v == d) return w;
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if (dist[v] <= w) continue;
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dist[v] = w;
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for (auto [u, ww] : g[v]) {
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if (dist_s[v] + ww + dist_d[u] <= best) continue; // pula essa aresta, corresponde a um caminho minimo
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if (dist[u] <= w + ww) continue;
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pq.push({-(w+ww), u});
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}
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}
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return -1;
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}
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int main(){
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ios::sync_with_stdio(0);
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cin.tie(0); cout.tie(0);
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int n, m;
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while (cin>>n>>m, n!=0 && m!=0){
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int s, d; cin >> s >> d;
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vector<vector<pll>> g(MAXN);
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vector<vector<pll>> g_rev(MAXN);
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for (int i=0;i<m;i++){
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int u,v,p; cin >> u >> v >> p;
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g[u].push_back({v, p});
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g_rev[v].push_back({u, p});
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}
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vector<ll> dist_s = dijk(s, g);
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vector<ll> dist_d = dijk(d, g_rev);
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cout << almost_dijk(s, d, g, dist_s, dist_d) << '\n';
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}
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} |