lintcode618- Search Graph Nodes- medium

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.

Notice

It's guaranteed there is only one available solution

Example

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

直接BFS。queue+set。API第一个给的graph冗余的不用管。

找一个最近的不用分层遍历，如果要你找到所有的话需要分层，取size套for。

/**
 * 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) {
        // write your code here
        if (graph == null || node == null || values == null) {
            return null;
        }
        Queue<UndirectedGraphNode> queue = new LinkedList<>();
        Set<UndirectedGraphNode> set = new HashSet<>();
        
        queue.offer(node);
        set.add(node);
        
        while (!queue.isEmpty()) {
            UndirectedGraphNode crt = queue.poll();
            if (values.get(crt) == target) {
                return crt;
            }
            for (UndirectedGraphNode neighbor : crt.neighbors) {
                if (!set.contains(neighbor)) {
                    queue.offer(neighbor);
                    set.add(neighbor);
                }
            }
        }
        return null;
    }
}