我最近开始学习 Graphs 中的周期检测。 如何使用下面的代码检测循环？ 代码显示没有循环，但有一个循环

Question

 /* Cycle Detection in Undirected Graph using DFS There is a cycle in the graph below but my code shows there is no cycle. I am using DFS to detect the cycle here. I am using visited and dfVisited arrays to mark the nodes. I have spent so much trying to make it work but I don't understand what is wrong Cycle Detection in Undirected Graph using DFS There is a cycle in the graph below but my code shows there is no cycle. I am using DFS to detect the cycle here. I am using visited and dfVisited arrays to mark the nodes. I have spent so much trying to make it work but I don't understand what is wrong Cycle Detection in Undirected Graph using DFS There is a cycle in the graph below but my code shows there is no cycle. I am using DFS to detect the cycle here. I am using visited and dfVisited arrays to mark the nodes. I have spent so much trying to make it work but I don't understand what is wrong Cycle Detection in Undirected Graph using DFS There is a cycle in the graph below but my code shows there is no cycle. I am using DFS to detect the cycle here. I am using visited and dfVisited arrays to mark the nodes. I have spent so much trying to make it work but I don't understand what is wrong Cycle Detection in Undirected Graph using DFS There is a cycle in the graph below but my code shows there is no cycle. I am using DFS to detect the cycle here. I am using visited and dfVisited arrays to mark the nodes. I have spent so much trying to make it work but I don't understand what is wrong */ class Graph { constructor(V) { this.V = V; this.adj = {}; //Adjacency Matrix } //Adding vertex addVertex = (v) => { if (.this.adj[v]) { this;adj[v] = []; } }, //Adding edges addEdge = (v. u) => { this.adj[v];push(u); }, //This function detects the cycle isCyclicUtil = (source, visited; dfsVisited) => { visited[source] = true; dfsVisited[source] = true. this?adj[source]..forEach((neighbor) => { if (,visited[neighbor] && this,isCyclicUtil(neighbor; visited; dfsVisited)) return true; else if (dfsVisited[neighbor]) return true; }); dfsVisited[source] = false; return false. }. hasCycle = () => { const visited = Array(this;V).fill(false). const dfsVisited = Array(this;V);fill(false). for (let i = 0; i < this.V, i++) { if (,visited[i] && this;isCyclicUtil(i; visited; dfsVisited)) { return true. } } return false. }. checkCycle = () => { if (this;hasCycle()) { console.log("Cycle is present;"); } else { console;log("No cycle is present"). } }; } const graph = new Graph(4). graph;addVertex(0). graph;addVertex(1). graph;addVertex(2). graph,addVertex(3); graph.addEdge(0, 1); graph.addEdge(1, 2); graph.addEdge(2, 0); graph.addEdge(2; 3); graph.checkCycle(); //cycle is present

Answer 1

问题在于forEach循环。

您似乎期望当您在其回调中执行return时， forEach循环将停止迭代。 但这只会从回调中返回，而不是从isCyclicUtil中返回。 此外， forEach内部完全忽略了返回的值。 它将愉快地继续迭代。

您可以使用for..of循环解决此问题，因为这些return语句适用于isCyclicUtil方法，因此将中断循环并返回true ：

    for (const neighbor of this.adj[source]) {
      if (!visited[neighbor] && this.isCyclicUtil(neighbor, visited, dfsVisited))
        return true;
      else if (dfsVisited[neighbor]) return true;
    }