DFS-----Route Between Two Nodes in Graph

最新推荐文章于 2024-11-22 16:56:04 发布

zjj2015

最新推荐文章于 2024-11-22 16:56:04 发布

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本文介绍了一种用于检测有向图中两个指定节点间是否存在路径的算法。通过深度优先搜索（DFS）方法实现，避免了循环并确保了算法效率。

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Given a directed graph, design an algorithm to find out whether there is a route between two nodes.

Have you met this question in a real interview? Yes
Example
Given graph:

A—–>B—–>C
\ |
\ |
\ |
\ v
->D—–>E
for s = B and t = E, return true

for s = D and t = C, return false

/**
 * Definition for Directed graph.
 * class DirectedGraphNode {
 *     int label;
 *     ArrayList<DirectedGraphNode> neighbors;
 *     DirectedGraphNode(int x) {
 *         label = x;
 *         neighbors = new ArrayList<DirectedGraphNode>();
 *     }
 * }
 */
public class Solution {
   /**
     * @param graph: A list of Directed graph node
     * @param s: the starting Directed graph node
     * @param t: the terminal Directed graph node
     * @return: a boolean value
     */
    public boolean hasRoute(ArrayList<DirectedGraphNode> graph,
                            DirectedGraphNode s, DirectedGraphNode t) {

        Set<DirectedGraphNode> visited = new HashSet<DirectedGraphNode>();
        return dfs(graph, s, t, visited);
    }

    public boolean dfs(ArrayList<DirectedGraphNode> graph,
                       DirectedGraphNode s, DirectedGraphNode t,
                       Set<DirectedGraphNode> visited) {

        if (s == t) {
            return true;
        } else {
            // corner cases
            if (s == null || t == null) return false;
            // flag visited node, avoid cylic
            visited.add(s);
            // compare unvisited neighbor nodes recursively
            if (s.neighbors.size() > 0) {
                for (DirectedGraphNode node : s.neighbors) {
                    if (visited.contains(node)) continue;
                    if (dfs(graph, node, t, visited)) return true;
                }
            }
        }

        return false;
    }
}