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52 lines
1.4 KiB
C++
52 lines
1.4 KiB
C++
#define _CRT_SECURE_NO_WARNINGS
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#define _SILENCE_CXX17_C_HEADER_DEPRECATION_WARNING
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#include <bits/stdc++.h>
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using namespace std;
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const int N = 200100;
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int adj[N], nxt[N], to[N], len[N], ecnt;
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int dis[N][2];
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struct node {
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int p, w;
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bool operator<(const node &rhs) const { return w > rhs.w; }
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};
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inline void addEdge(int f, int t, int l) {
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ecnt++;
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nxt[ecnt] = adj[f];
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adj[f] = ecnt;
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to[ecnt] = t;
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len[ecnt] = l;
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}
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int main() {
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int T, n, m;
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scanf("%d", &T);
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while (T--) {
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memset(dis, 0x3f, sizeof(dis));
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scanf("%d%d", &n, &m);
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for (int i = 0, u, v, w; i < m; i++)
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scanf("%d%d%d", &u, &v, &w), addEdge(u, v, w), addEdge(v, u, w);
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priority_queue<node> H;
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dis[1][0] = 0;
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H.push({1, 0});
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while (!H.empty()) {
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auto x = H.top();
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H.pop();
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for (int e = adj[x.p]; e; e = nxt[e]) {
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if (dis[to[e]][0] >= dis[x.p][0] + len[e]) {
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dis[to[e]][1] = dis[to[e]][0];
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dis[to[e]][0] = dis[x.p][0] + len[e];
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H.push({to[e], dis[to[e]][0]});
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} else if (dis[to[e]][1] >= dis[x.p][0] + len[e])
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dis[to[e]][1] = dis[x.p][0] + len[e];
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}
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}
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printf("%d\n", dis[n][1]);
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}
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return 0;
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}
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