一、Edge边表示、判断负环

       注意这里的图一般用有向图表示 也就是说 1 – 2， 2 – 1 如果权重为负值  那么 也算有负权环（这里表示了添加两条边的方法）

       这里因为添加双向边 则 一旦有负w出现就会认为是负权环

import java.util.Scanner;

public class Main {
    static Edge []edges;
    static boolean []visit;
    static int n, m;
    static int tol;
    static int[]dis;
    static int INF = 9999999;
    static int[]head;
    static boolean hasNegCycle = false;
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        while(in.hasNext()) {
            n = in.nextInt();
            m = in.nextInt();
            if(n == 0 && m == 0)
                break;
            edges = new Edge[2*m+1];
            for(int i = 1; i <= 2*m; i++ )
                edges[i] = new Edge();
            tol = 1;
            head = new int[n+1];
            dis = new int[n+1];
            for(int i = 1; i <= n; i++ )
                head[i] = -1;
            for(int i = 1; i <= m; i++ ) {
                int u = in.nextInt();
                int v = in.nextInt();
                int w = in.nextInt();
                add(u, v, w);
                add(v, u, w);
            }
            bell_man();
            if(!hasNegCycle) {
                System.out.println(dis[n]);
            }
            else
                System.out.println("hasNegtiveCycle");
//			for(int i = 1; i < tol; i++ ) {
//				Edge e = edges[i];
//				System.out.println(e.from + " " + e.to + " " + e.w);
//			}
        }
        
    }
    public static void bell_man() {
        
        for(int i = 1; i <= n; i++ ) {
            dis[i] = (i == 1) ? 0 : INF;
        }
        
        for(int i = 1; i < n; i++ ) {
            int flag = 0;
            for(int j = 1; j <= 2*m; j++ ) {
                Edge e = edges[j];
                if(dis[e.to] > dis[e.from] + e.w) {
                    flag = 1;
                    dis[e.to] = dis[e.from] + e.w;
                }
            }
            if(flag == 0)
                break;
        }
        hasNegCycle = false;
        for(int i = 1; i <= 2*m; i++ ) {
            Edge e = edges[i];
            if(dis[e.to] > dis[e.from] + e.w) {
                hasNegCycle = true;
                break;
            }
        }
    }
    public static void add(int from, int to, int w) {
        edges[tol].from = from;
        edges[tol].to = to;
        edges[tol].w = w;
        edges[tol].next = head[from];
        head[from] = tol++;
    }

}

class Edge{
    int from, to;
    int w;
    int next;
//	public Edge(int from, int to) {
//		this.from = from;
//		this.to = to;
//		this.w = w;
//	}
}