mirror of
https://git.sb/baoshuo/OI-codes.git
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91 lines
1.7 KiB
C++
91 lines
1.7 KiB
C++
#include <iostream>
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#include <cstring>
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#include <deque>
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#include <set>
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#include <vector>
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using std::cin;
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using std::cout;
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const char endl = '\n';
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const int N = 1000005;
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int n, m, id[N], last[N], dist[N];
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bool vis[N];
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std::set<int> cs;
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std::vector<std::pair<int, int>> c[N], g[N];
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void bfs() {
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memset(dist, 0x3f, sizeof(dist));
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std::deque<int> q;
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dist[1] = 0;
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q.emplace_back(1);
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while (!q.empty()) {
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int u = q.front();
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q.pop_front();
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if (vis[u]) continue;
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vis[u] = true;
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for (auto e : g[u]) {
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int v = e.first,
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w = e.second;
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if (dist[v] > dist[u] + w) {
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dist[v] = dist[u] + w;
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if (w) q.emplace_back(v);
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else q.emplace_front(v);
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}
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}
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}
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}
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int main() {
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std::ios::sync_with_stdio(false);
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cin.tie(nullptr);
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cin >> n >> m;
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for (int i = 1, u, v, c; i <= m; i++) {
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cin >> u >> v >> c;
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::c[c].emplace_back(u, v);
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cs.insert(c);
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}
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int cnt = n;
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for (int x : cs) {
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for (auto e : c[x]) {
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int u = e.first,
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v = e.second;
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if (last[u] != x) {
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last[u] = x;
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id[u] = ++cnt;
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g[u].emplace_back(id[u], 1);
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g[id[u]].emplace_back(u, 0);
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}
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if (last[v] != x) {
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last[v] = x;
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id[v] = ++cnt;
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g[v].emplace_back(id[v], 1);
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g[id[v]].emplace_back(v, 0);
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}
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g[id[u]].emplace_back(id[v], 0);
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g[id[v]].emplace_back(id[u], 0);
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}
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}
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bfs();
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cout << (dist[n] == 0x3f3f3f3f ? -1 : dist[n]) << endl;
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return 0;
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}
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