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https://git.sb/baoshuo/OI-codes.git
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51 lines
1.2 KiB
C++
51 lines
1.2 KiB
C++
#include <bits/stdc++.h>
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using namespace std;
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int t, n, m, u, v, w, cnt, dist[2005];
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bool flag;
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struct node {
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int u, v, w;
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node() {
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u = v = w = 0;
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}
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node(int _u, int _v, int _w) {
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u = _u;
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v = _v;
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w = _w;
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}
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} g[6005];
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int main() {
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cin >> t;
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while (t--) {
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cnt = 0;
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flag = false;
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memset(g, 0x00, sizeof(g));
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memset(dist, 0x3f, sizeof(dist));
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cin >> n >> m;
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for (int i = 1; i <= m; i++) {
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cin >> u >> v >> w;
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g[++cnt] = node(u, v, w);
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if (w >= 0) g[++cnt] = node(v, u, w);
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}
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dist[1] = 0;
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for (int i = 1; i <= n; i++) {
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for (int j = 1; j <= cnt; j++) {
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if (dist[g[j].u] == 0x3f3f3f3f) continue;
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dist[g[j].v] = min(dist[g[j].v], dist[g[j].u] + g[j].w);
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}
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}
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for (int i = 1; i <= cnt; i++) {
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if (dist[g[i].u] == 0x3f3f3f3f || dist[g[i].v] == 0x3f3f3f3f) continue;
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if (dist[g[i].v] > dist[g[i].u] + g[i].w) {
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flag = true;
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}
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}
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cout << (flag ? "YES" : "NO") << endl;
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}
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return 0;
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}
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