Search Graph Nodes_search graph nodes leetcode-优快云博客

本文链接：https://blog.youkuaiyun.com/u013325815/article/details/103650608

本文深入探讨了图搜索算法中的一种应用场景——寻找具有特定目标值的最近节点。通过BFS算法结合visited集合避免环路，有效地在无向图中找到了目标节点。文章提供了详细的代码示例和两个具体例子，帮助读者理解算法的实现过程。

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Given a undirected graph, a node and a target, return the nearest node to given node which value of it is target, return NULL if you can't find.

There is a mapping store the nodes' values in the given parameters.

Example

Example 1:

Input:
{1,2,3,4#2,1,3#3,1,2#4,1,5#5,4}
[3,4,5,50,50]
1
50
Output:
4
Explanation:
2------3  5
 \     |  | 
  \    |  |
   \   |  |
    \  |  |
      1 --4
Give a node 1, target is 50

there a hash named values which is [3,4,10,50,50], represent:
Value of node 1 is 3
Value of node 2 is 4
Value of node 3 is 10
Value of node 4 is 50
Value of node 5 is 50

Return node 4

Example 2:

Input:
{1,2#2,1}
[0,1]
1
1
Output:
2

Notice

It's guaranteed there is only one available solution

思路：就bfs用visited来避免环。graph参数没用，直接用node开始搜就可以了。

/**
 * Definition for graph node.
 * class UndirectedGraphNode {
 *     int label;
 *     ArrayList<UndirectedGraphNode> neighbors;
 *     UndirectedGraphNode(int x) { 
 *         label = x; neighbors = new ArrayList<UndirectedGraphNode>(); 
 *     }
 * };
 */


public class Solution {
    /*
     * @param graph: a list of Undirected graph node
     * @param values: a hash mapping, <UndirectedGraphNode, (int)value>
     * @param node: an Undirected graph node
     * @param target: An integer
     * @return: a node
     */
    public UndirectedGraphNode searchNode(ArrayList<UndirectedGraphNode> graph,
                                          Map<UndirectedGraphNode, Integer> values,
                                          UndirectedGraphNode node,
                                          int target) {
        if(node == null) {
            return null;
        }
        
        Queue<UndirectedGraphNode> queue = new LinkedList<UndirectedGraphNode>();
        HashSet<UndirectedGraphNode> visited = new HashSet<UndirectedGraphNode>();
        
        queue.offer(node);
        visited.add(node);
        
        while(!queue.isEmpty()){
            UndirectedGraphNode n = queue.poll();
            if(values.get(n) == target) {
                return n;
            }
            for(UndirectedGraphNode neighbor: n.neighbors) {
                if(!visited.contains(neighbor)){
                    visited.add(neighbor);
                    queue.offer(neighbor);
                }
            }
        }
        return null;
    }
}