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59 lines
1.3 KiB
59 lines
1.3 KiB
#include <bits/stdc++.h>
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using namespace std;
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const int N = 2010, M = 10010;
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int n, m; // 点数、边数
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int d[N]; // 存储每个点到1号点的最短距离
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bool st[N]; // 存储每个点是否在队列中
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int cnt[N]; //
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// 邻接表
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int e[M], h[N], idx, w[M], ne[M];
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void add(int a, int b, int c) {
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e[idx] = b, ne[idx] = h[a], w[idx] = c, h[a] = idx++;
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}
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int spfa() {
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queue<int> q;
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// 构建超级源点，防止负环与出发点不连通
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for (int i = 1; i <= n; i++) {
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q.push(i);
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st[i] = true;
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}
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while (q.size()) {
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int u = q.front();
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q.pop();
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st[u] = 0;
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for (int i = h[u]; ~i; i = ne[i]) {
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int v = e[i];
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if (d[v] > d[u] + w[i]) {
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d[v] = d[u] + w[i];
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cnt[v] = cnt[u] + 1;
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if (cnt[v] >= n) return 1;
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if (!st[v]) {
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q.push(v);
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st[v] = 1;
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}
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}
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}
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}
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return 0;
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}
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int main() {
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memset(h, -1, sizeof h);
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cin >> n >> m;
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while (m--) {
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int a, b, c;
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cin >> a >> b >> c;
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add(a, b, c);
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}
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// 调用spfa判断是否有负环
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if (spfa())
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puts("Yes");
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else
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puts("No");
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return 0;
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} |