dijkstra单源最短路径算法不允许边权值为负，适用的图范围可以很大。
代码如下：

#include <iostream>
#include <queue>
#include <vector>
#include <string>
using namespace std;
const int N = 1e8;
bool done[N];
int dis[N];
const int INF = 1 << 30;
int n, m;struct edge {int from;int to;int w;
};
vector<edge>e[N];struct node {int id;int dis;friend bool operator<(const node &a, const node &b) {return a.dis > b.dis;}
};void dijkstra(int s) //s为起点
{priority_queue<node>q;memset(done, 0, sizeof(done));for (int i = 1; i <= n; i++)dis[i] = INF;memset(done, 0, sizeof(done));dis[s] = 0;q.push({s, dis[s]});while (q.size()) {node t = q.top();q.pop();if (done[t.id])continue;done[t.id] = true;for (int i = 0; i < e[t.id].size(); i++) {edge y = e[t.id][i];if (done[y.to])continue;if (dis[y.to] > y.w + t.dis) {dis[y.to] = y.w + t.dis;q.push({y.to, dis[y.to]});}}}
}int main() {while (cin >> n >> m, n, m) {for (int i = 1; i <= n; i++)e[i].clear();while (m--) {int a, b, c;cin >> a >> b >> c;e[a].push_back({a, b, c});e[b].push_back({b, a, c});}int start;cin >> start;//起点dijkstra(start);int no;while (cin >> no, no)//询问no点到起点的距离{cout << dis[no] << endl;}}return 0;
}