Bellman-Ford模板

Dijkstra算法无法判断含负权边的图的最短路。如果遇到负权，在没有负权回路存在时（负权回路的含义是，回路的权值和为负。）即便有负权的边，也可以采用Bellman-Ford算法正确求出最短路径。

主要是做N次松弛，用变量记录入队列的次数和是否入过队列，如果每次都如队列则判定有负环

#include 
#include 
#include 
#include 
#include 
#include 
using namespace std;
#define maxn 1000
#define INF 1<<30
struct Edge{
    int from , to ,val;
    Edge(int from,int to,int val) : from(from),to(to),val(val){}
};
int m , n , dest;
int d[maxn],p[maxn];
vector edges;
vector G[maxn];
void init(int n) {
    for(int i = 0;i< n;i++) G[i].clear();
    edges.clear();
}
void addEdge(int from,int to,int val) {
    edges.push_back(Edge(from,to,val));
    m = edges.size();
    G[from].push_back(m - 1);
}

bool bellman_ford (int s) {
    for(int i = 0;i<= m;i++) d[i] = INF;
    d[s] = 0;
    for(int i = 0;i< n;i++) {
        bool change = false;
        for(int j = 0; j<= m;j++) {
            Edge e = edges[j];
            if(d[e.to] > d[e.from] + e.val && d[e.from] < INF) {
                d[e.to] = d[e.from] + e.val;
                p[e.to] = j;
                change = true;
            }
        }
        if(!change) return true;
        if(i == n-1 && change)return false;
    }
    return false;
}
void print(int end) {
    Edge e = edges[p[end]];
    if(end == 1) {
        printf("%d(%d)",e.from,0);
        return;
    }
    if(e.from != end) {
        print(e.from);
        printf("->%d(%d)",e.to,e.val);
    }
}
int main()
{
    freopen("in.txt","r",stdin);
    while(~scanf("%d%d",&n,&m) && n> 0) {
        init(n);
        int from,to ,val;
        for(int i = 0 ;i< n;i++) {
            scanf("%d%d%d",&from,&to,&val);
            addEdge(from,to,val);
        }
        if(bellman_ford(1)) {
            print(m);
            cout<