Route Between Two Nodes in Graph（図中の2点間の路線）

http://www.lintcode.com/en/problem/route-between-two-nodes-in-graph/?rand=true
解析はClone Graph（クローン図）を参照してください。

/**
 * Definition for Directed graph.
 * class DirectedGraphNode {
 * int label;
 * ArrayList neighbors;
 * DirectedGraphNode(int x) {
 * label = x;
 * neighbors = new ArrayList();
 * }
 * };
 */
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 graph,
                            DirectedGraphNode s, DirectedGraphNode t) {
        // write your code here
        if (s == t) {
            return true;
        }
        //    list        。           
        ArrayList visited = new ArrayList<>();
        visited.add(s);
        for (int i = 0; i < visited.size(); i++) {
            DirectedGraphNode node = visited.get(i);
            for (DirectedGraphNode temp : node.neighbors) {
                if (temp == t) {
                    return true;
                }
                if (visited.contains(temp)) {
                    continue;
                }
                visited.add(temp);
            }
        }
        return false;
    }
}