SPFA算法

hdoj 2544链接

import java.util.LinkedList;import java.util.Queue;import java.util.Scanner;public class Main {static boolean []visit;static int []u;static int []v;static int []w;static int []head;static int []next;static int []dist;static int m, n;static int INF = 99999999;static Queue<Integer> que;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;u = new int[2*m+1];//边数多一 因为从1开始v = new int[2*m+1];w = new int[2*m+1];next = new int[2*m+1];dist = new int[n+1];//顶点多一head = new int[n+1];visit = new boolean[n+1];que = new LinkedList<>();for(int i = 0; i <= n; i++ ) {head[i] = -1;}for(int i = 1; i <= m; i++ ) {u[i] = in.nextInt();v[i] = in.nextInt();w[i] = in.nextInt();next[i] = head[u[i]];head[u[i]] = i;}for(int i = m+1; i <= 2*m; i++ ) {//构建 无向图u[i] = v[i-m];v[i] = u[i-m];w[i] = w[i-m];next[i] = head[u[i]];head[u[i]] = i;}spfa();System.out.println(dist[n]);}}public static void spfa() {for(int i = 1; i <= n; i++ ) {dist[i] = INF;}dist[1] = 0;visit[1] = true;que.offer(1);while(!que.isEmpty()) {int from = que.poll();visit[from] = false;//出队后 标记为未访问int k = head[from];while(k != -1) {if(dist[v[k]] > dist[u[k]] + w[k]) {dist[v[k]] = dist[u[k]] + w[k];if(!visit[v[k]]) {que.offer(v[k]);}}k = next[k];//寻找下一条边}}}}