无环有向图最长路径

1、把dist 初始为负无穷

2、松弛判断条件改为 dist[v] < dist[u] + w;

import java.util.ArrayList;import java.util.Scanner;import java.util.Stack;import Graph.HasCycle;import javafx.scene.effect.Light.Distant;public class TopDij {static boolean[]visit;static boolean[]onStack;static Stack<Integer> stack;static int n, m;static boolean hasCycle = false;static int[]dis;static int INF = 99999999;static ArrayList<EdgeS> []adj;public static void main(String[] args) {Scanner in = new Scanner(System.in);n = in.nextInt();m = in.nextInt();visit = new boolean[n+1];adj = new ArrayList[n+1];stack = new Stack<>();dis = new int[n+1];onStack = new boolean[n+1];for(int i = 1; i <= n; i++ ) {adj[i] = new ArrayList<>();}for(int i = 0; i < m; i++ ) {int from = in.nextInt();int to = in.nextInt();int w = in.nextInt();adj[from].add(new EdgeS(from, to, w));}bfs(1);if(!hasCycle) {shortPath(1);System.out.println(dis[3]);}else {System.out.println("hasCycle");}}public static void shortPath(int s) {for(int i = 1; i <= n; i++ ) {dis[i] = -INF;}dis[s] = 0;while(!stack.isEmpty()) {int cur = stack.pop();for(EdgeS e: adj[cur]) {if(dis[e.to] < dis[cur] + e.w) {dis[e.to] = dis[cur] + e.w;}}}}public static void bfs(int cur) {visit[cur] = true;onStack[cur] = true;for(EdgeS e:adj[cur]) {if(!visit[e.to]) {bfs(e.to);}else if(onStack[e.to]){hasCycle = true;return;}}onStack[cur] = false;stack.push(cur);}}class EdgeS{int from, to, w;public EdgeS(int f, int t, int w) {from = f;to = t;this.w = w;}}