43 lines
1.1 KiB
C++
43 lines
1.1 KiB
C++
#include <bits/stdc++.h>
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using namespace std;
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const int INF = 0x3f3f3f3f;
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const int N = 2510; //结点数
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const int M = 6200 * 2 + 10; //边数
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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 n, m; // n个结点，m条边
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int s, t; //起点，终点
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int d[N]; //距离数组
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void bellman_ford(int start) {
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memset(d, 0x3f, sizeof d);
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d[start] = 0;
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int T = n - 1; //常规的Bellman_Ford是执行n-1次
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while (T--) { //松驰n-1次
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for (int k = 1; k <= n; k++) //枚举1~n节点
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for (int i = h[k]; ~i; i = ne[i]) { //二层循环枚举每个节点的出边
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int j = e[i];
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d[j] = min(d[j], d[k] + w[i]);
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}
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}
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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 >> s >> t;
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for (int i = 0; i < m; i++) {
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int a, b, c;
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cin >> a >> b >> c;
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add(a, b, c), add(b, a, c);
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}
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bellman_ford(s);
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cout << d[t] << endl;
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return 0;
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}
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