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package airbnb;

import java.util.HashMap;
import java.util.HashSet;
import java.util.LinkedList;
import java.util.List;
import java.util.PriorityQueue;
import java.util.Queue;



public class ShortestPath {

	public static void main(String[] args) {
		List<List<Integer>> relations = new LinkedList<>();
		for (int i = 0; i < 9; i++) {
			relations.add(new LinkedList<>());
			switch (i) {
				case 0: relations.get(i).add(1);relations.get(i).add(4);break;
				case 1: relations.get(i).add(2);break;
				case 2: relations.get(i).add(3);break;
				case 3: relations.get(i).add(4);break;
				case 4: relations.get(i).add(5);relations.get(i).add(9);break;
				case 5: relations.get(i).add(6);break;
				case 6: relations.get(i).add(7);break;
				case 7: relations.get(i).add(8);break;
				case 8: relations.get(i).add(9);break;
				case 9: relations.get(i).add(0);break;
			}
		}
		ShortestPath path = new ShortestPath();
		List<Node> res = path.findShortestPath(relations, 0, 9);
		for (Node node : res) {
			System.out.println(node.person);
		}
	}
	
	public List<Node> findShortestPath(List<List<Integer>> relations, int start, int target) {
		if (relations == null || relations.size() < 0) {
			return null;
		}
		HashMap<Integer, Node> map = new HashMap<>();
		for (int i = 0; i < relations.size(); i++) {
			Node person;
			if (map.containsKey(i)) {
				person = map.get(i);
			} else {
				person = new Node(i);
				map.put(i, person);
			}
			if (i == start) {
				person.minCost = 0;
				person.minPath.add(person);
			}
			for (Integer integer : relations.get(i)) {
				Node after = map.getOrDefault(integer, new Node(integer));
				map.put(integer, after);
				person.frontier.add(after);
			}
		}
		
		dijkstra(map, start, target);
		return map.get(target).minPath;
	}
	
	public void dijkstra(HashMap<Integer, Node> map, int start, int target) {
		PriorityQueue<Node> frontiers = new PriorityQueue<>((a,b) -> (a.minCost - b.minCost));
		Node startNode = map.get(start);
		for (Node next : startNode.frontier) {
			next.minCost = (next.person - startNode.person) * (next.person - startNode.person);
			next.minPath = new LinkedList<>(startNode.minPath);
			next.minPath.add(next);
			frontiers.add(next);
		}
		while (!frontiers.isEmpty()) {
			Node cur = frontiers.poll();
			for (Node next : cur.frontier) {
				int oldCost = next.minCost;
				int cost = cur.minCost + (next.person - cur.person) * (next.person - cur.person);
				if (cost < next.minCost) {
					next.minCost = cost;
					next.minPath = new LinkedList<>(cur.minPath);
					next.minPath.add(next);
				}
				if (oldCost == Integer.MAX_VALUE) {
					frontiers.add(next);
				}
			}
		}
	}
	
	public class Node {
		int person;
		int minCost;
		List<Node> minPath;
		List<Node> frontier;
		
		public Node(int person) {
			this.person = person;
			minCost = Integer.MAX_VALUE;
			minPath = new LinkedList<>();
			frontier = new LinkedList<>();
		}
	}

}