Java问题集锦--经典面试题（2）

附图中有一个无向图，其中圈内数字代表一个地点，边 e 上数字代表长度 Le （双向相同）。一位外卖小哥在起点 A ，要去 3 个商家（B1，B2，B3）取餐，送到3个对应的地方（C1，C2，C3），即 B1至C1，B2至C2，B3至C3。小哥的电动助力车的箱子同时最多装下2份外卖。

请问：小哥该怎么走路径最短？这个最短路径的长度是多少？这里，A是出发点，最后一餐（不限次序）送达地为终点。为了简化问题，假设商家已经备好了外卖，小哥取餐送餐不用等。又假设每份外卖重量大小一样。

我的解题思路是：先写一个方法用来求出任意两个地点之间的最短路径，然后再对取快递和送快递可能出现的不同次序的情况进行穷举，挨个求出每种情况的路径总长度，从中取出路径总长度最短的路径。

import java.util.HashMap;
import java.util.Map;

/**
 * 地点
 */
public class Location {

	// 地点编号
	private Integer id;

	// 该地点可以到达的其他地点及其距离<可以到达的地点编号,到达该地点的距离>
	private Map reachMap = new HashMap();

	// 此处省略get和set方法

	@Override
	public String toString() {
		return "地点编号：" + id;
	}

	@Override
	public boolean equals(Object obj) {
		Location that = (Location) obj;
		return this.id == that.id;
	}
}

import java.util.ArrayList;
import java.util.HashSet;
import java.util.List;
import java.util.Set;

/**
 * 外卖路线
 */
public class Route implements Comparable {

	// 路线总距离
	private Integer distance = 0;

	// 路线经过的地点
	private List locations = new ArrayList();

	// 路线已经经过的地点，去重用，防止出现死循环
	private Set passedLocations = new HashSet();

	// 此处省略get和set方法

	@Override
	public String toString() {
		Integer size = locations.size();
		String str = "从位置[ " + locations.get(0) + " ]到位置[ " + locations.get(size - 1) + " ]路线距离：" + distance + "\n"
				+ "路线如下：" + "\n";
		for (int i = 0; i < size; i++) {
			str += "-->" + locations.get(i).getId().toString();
		}
		return str;
	}

	@Override
	public int compareTo(Route that) {
		return this.distance - that.distance;
	}
}

import java.util.ArrayList;
import java.util.List;

/**
 * 外卖的取/送策略
 */
public class DeliveryStrategy implements Comparable {

	// 外卖的取/送顺序
	private List locationsOrder = new ArrayList();

	// 当前已经领取，但还未送出的外卖地点编号列表
	private List fetchedLocations = new ArrayList();

	// 待领取的外卖地点编号列表
	private List locations2Fetch = new ArrayList();

	// 还未送达的外卖地点编号列表
	private List locations2Send = new ArrayList();

	// 该策略最短路线的路程
	private Integer distance = 0;

	// 此处省略get和set方法

	@Override
	public int compareTo(DeliveryStrategy that) {
		return this.distance - that.distance;
	}

	@Override
	public String toString() {
		String str = "策略：\n";
		for (Integer index : locationsOrder) {
			str += "==>" + index;
		}

		return str;
	}
}

import java.util.ArrayList;
import java.util.Collections;
import java.util.HashMap;
import java.util.HashSet;
import java.util.Iterator;
import java.util.List;
import java.util.Map;
import java.util.Map.Entry;
import java.util.Set;

public class MainClass {

	// 最多一次性取几个外卖
	public static Integer deliverCount = 2;

	// 所有的地点数据信息
	public Map locations = new HashMap();

	// 初始化地点数据信息
	public void initLocations() {
		Location l1 = new Location();
		l1.setId(1);
		l1.getReachMap().put(2, 1);
		l1.getReachMap().put(5, 1);

		Location l2 = new Location();
		l2.setId(2);
		l2.getReachMap().put(1, 1);
		l2.getReachMap().put(3, 2);
		l2.getReachMap().put(6, 2);

		Location l3 = new Location();
		l3.setId(3);
		l3.getReachMap().put(2, 2);
		l3.getReachMap().put(4, 1);
		l3.getReachMap().put(8, 2);

		Location l4 = new Location();
		l4.setId(4);
		l4.getReachMap().put(3, 1);
		l4.getReachMap().put(15, 3);

		Location l5 = new Location();
		l5.setId(5);
		l5.getReachMap().put(1, 1);
		l5.getReachMap().put(6, 1);
		l5.getReachMap().put(9, 1);

		Location l6 = new Location();
		l6.setId(6);
		l6.getReachMap().put(2, 2);
		l6.getReachMap().put(5, 1);
		l6.getReachMap().put(7, 1);

		Location l7 = new Location();
		l7.setId(7);
		l7.getReachMap().put(6, 1);
		l7.getReachMap().put(8, 1);
		l7.getReachMap().put(10, 1);

		Location l8 = new Location();
		l8.setId(8);
		l8.getReachMap().put(3, 2);
		l8.getReachMap().put(7, 1);
		l8.getReachMap().put(11, 1);

		Location l9 = new Location();
		l9.setId(9);
		l9.getReachMap().put(5, 1);
		l9.getReachMap().put(10, 3);
		l9.getReachMap().put(12, 2);

		Location l10 = new Location();
		l10.setId(10);
		l10.getReachMap().put(7, 1);
		l10.getReachMap().put(9, 3);
		l10.getReachMap().put(11, 1);
		l10.getReachMap().put(13, 2);

		Location l11 = new Location();
		l11.setId(11);
		l11.getReachMap().put(8, 1);
		l11.getReachMap().put(10, 1);
		l11.getReachMap().put(14, 1);

		Location l12 = new Location();
		l12.setId(12);
		l12.getReachMap().put(9, 2);
		l12.getReachMap().put(13, 2);

		Location l13 = new Location();
		l13.setId(13);
		l13.getReachMap().put(10, 2);
		l13.getReachMap().put(12, 2);
		l13.getReachMap().put(14, 1);

		Location l14 = new Location();
		l14.setId(14);
		l14.getReachMap().put(11, 1);
		l14.getReachMap().put(13, 1);
		l14.getReachMap().put(15, 1);

		Location l15 = new Location();
		l15.setId(15);
		l15.getReachMap().put(4, 3);
		l15.getReachMap().put(14, 1);

		locations.put(1, l1);
		locations.put(2, l2);
		locations.put(3, l3);
		locations.put(4, l4);
		locations.put(5, l5);
		locations.put(6, l6);
		locations.put(7, l7);
		locations.put(8, l8);
		locations.put(9, l9);
		locations.put(10, l10);
		locations.put(11, l11);
		locations.put(12, l12);
		locations.put(13, l13);
		locations.put(14, l14);
		locations.put(15, l15);
	}

	// 获取编号 start 和编号 end 两个地点之间的最短路线
	public Route getNearestRoute(Integer start, Integer stop) {
		Location startLocation = locations.get(start);
		Location stopLocation = locations.get(stop);
		Route route = new Route();
		route.getLocations().add(startLocation);
		route.getPassedLocations().add(startLocation);

		List routesList = new ArrayList();
		routesList.add(route);
		List routes = getRoutes(routesList, stopLocation);
		Collections.sort(routes);
		Route nearestRoute = routes.get(0);
		return nearestRoute;
	}

	// 获取能够到达指定地点的所有路线
	public List getRoutes(List startRoutes, Location endLocation) {
		List returnRoutes = new ArrayList();

		for (int i = 0; i < startRoutes.size(); i++) {
			Route parentRoute = startRoutes.get(i);
			Integer parentDistance = parentRoute.getDistance();
			List parentLocations = parentRoute.getLocations();
			Set parentPassedLocations = parentRoute.getPassedLocations();
			Location parentLastLocation = parentLocations.get(parentLocations.size() - 1);

			if (parentLastLocation.equals(endLocation)) {
				returnRoutes.add(parentRoute);
			} else {
				Iterator> it = parentLastLocation.getReachMap().entrySet().iterator();
				while (it.hasNext()) {
					Map.Entry entry = it.next();
					Integer locationId = entry.getKey();
					Integer distance = entry.getValue();
					Route r = new Route();
					r.setLocations(new ArrayList(parentLocations));
					r.setPassedLocations(new HashSet(parentPassedLocations));
					r.setDistance(parentDistance);
					Location thisLocation = locations.get(locationId);
					if (parentPassedLocations.contains(thisLocation)) {
						continue;
					}
					r.getLocations().add(thisLocation);
					r.getPassedLocations().add(thisLocation);
					r.setDistance(r.getDistance() + distance);
					if (thisLocation.equals(endLocation)) {
						returnRoutes.add(r);
					} else {
						List list2 = new ArrayList();
						list2.add(r);
						returnRoutes.addAll(getRoutes(list2, endLocation));
					}
				}
			}
		}
		return returnRoutes;
	}

	// 获取所有的外卖路线策略
	public List getAllDeliveryStrategy(Map map) {
		Map reverseMap = new HashMap();
		for (Entry entry : map.entrySet()) {
			reverseMap.put(entry.getValue(), entry.getKey());
		}
		return getAllDeliveryStrategy(map, reverseMap);
	}

	// 获取所有的外卖路线策略
	public List getAllDeliveryStrategy(Map map, Map reverseMap) {
		List startLocations = new ArrayList();
		for (Integer key : map.keySet()) {
			startLocations.add(key);
		}
		List endLocations = new ArrayList();
		for (Integer val : map.values()) {
			endLocations.add(val);
		}

		DeliveryStrategy delivery = new DeliveryStrategy();
		delivery.getLocations2Fetch().addAll(startLocations);
		delivery.getLocations2Send().addAll(endLocations);
		List allDelivery = getAllDeliveryStrategy(null, delivery, map, reverseMap);
		return allDelivery;
	}

	// 获取所有的外卖路线策略
	public List getAllDeliveryStrategy(List deliveryStrategyList,
			DeliveryStrategy delivery, Map map, Map reverseMap) {
		List fetchedLocations = delivery.getFetchedLocations();
		List locations2Fetch = delivery.getLocations2Fetch();
		List locations2Send = delivery.getLocations2Send();
		List strategyLocations = delivery.getLocationsOrder();
		if (null == deliveryStrategyList) {
			deliveryStrategyList = new ArrayList();
		}

		// 当前未领取任何外卖
		if (fetchedLocations.isEmpty()) {
			// 没有任何外卖待领取
			if (locations2Fetch.isEmpty()) {
				DeliveryStrategy strategy = new DeliveryStrategy();
				strategy.getLocationsOrder().addAll(strategyLocations);
				strategy.getLocations2Send().addAll(locations2Send);
				strategy.getLocations2Fetch().addAll(locations2Fetch);
				deliveryStrategyList.add(strategy);
			} else {
				// 有外卖待领取
				for (Integer start : locations2Fetch) {
					DeliveryStrategy strategy = new DeliveryStrategy();
					strategy.getLocationsOrder().addAll(strategyLocations);
					strategy.getLocations2Send().addAll(locations2Send);
					strategy.getLocations2Fetch().addAll(locations2Fetch);
					strategy.getLocationsOrder().add(start);
					strategy.getFetchedLocations().add(start);
					strategy.getLocations2Fetch().remove(start);
					getAllDeliveryStrategy(deliveryStrategyList, strategy, map, reverseMap);
				}
			}
		} else {
			// 当前已领取的外卖数小于deliverCount
			if (fetchedLocations.size() < deliverCount) {
				// 先送一个
				for (Integer fetch : fetchedLocations) {
					DeliveryStrategy strategy = new DeliveryStrategy();
					strategy.getLocationsOrder().addAll(strategyLocations);
					strategy.getLocations2Send().addAll(locations2Send);
					strategy.getLocations2Fetch().addAll(locations2Fetch);
					strategy.getFetchedLocations().addAll(fetchedLocations);
					Integer tempEndLocation = map.get(fetch);
					strategy.getLocationsOrder().add(tempEndLocation);
					strategy.getFetchedLocations().remove(fetch);
					strategy.getLocations2Send().remove(tempEndLocation);
					getAllDeliveryStrategy(deliveryStrategyList, strategy, map, reverseMap);
				}

				// 先取一个
				for (Integer startIndex : locations2Fetch) {
					DeliveryStrategy strategy = new DeliveryStrategy();
					strategy.getLocationsOrder().addAll(strategyLocations);
					strategy.getLocations2Send().addAll(locations2Send);
					strategy.getLocations2Fetch().addAll(locations2Fetch);
					strategy.getFetchedLocations().addAll(fetchedLocations);

					strategy.getLocationsOrder().add(startIndex);
					strategy.getFetchedLocations().add(startIndex);
					strategy.getLocations2Fetch().remove(startIndex);
					getAllDeliveryStrategy(deliveryStrategyList, strategy, map, reverseMap);
				}

			} else {

				// 当前已领取的外卖数达到deliverCount,只能先送
				for (Integer fetch : fetchedLocations) {
					DeliveryStrategy strategy = new DeliveryStrategy();
					strategy.getLocationsOrder().addAll(strategyLocations);
					strategy.getLocations2Send().addAll(locations2Send);
					strategy.getLocations2Fetch().addAll(locations2Fetch);
					strategy.getFetchedLocations().addAll(fetchedLocations);

					Integer tempEndLocation = map.get(fetch);
					strategy.getLocationsOrder().add(tempEndLocation);
					strategy.getFetchedLocations().remove(fetch);
					strategy.getLocations2Send().remove(tempEndLocation);
					getAllDeliveryStrategy(deliveryStrategyList, strategy, map, reverseMap);
				}
			}
		}
		return deliveryStrategyList;
	}

	public static void main(String[] args) {
		MainClass m = new MainClass();
		m.initLocations();
		Map map = new HashMap();
		map.put(3, 12);
		map.put(7, 11);
		map.put(4, 13);

		Integer startIndex = 2;

		List allRoutes = m.getAllDeliveryStrategy(map);

		for (DeliveryStrategy strategy : allRoutes) {
			List deliveryPoints = strategy.getLocationsOrder();
			Integer distance = 0;

			Integer newStart = startIndex;
			for (Integer index : deliveryPoints) {
				Route nearestRoute = m.getNearestRoute(newStart, index);
				distance += nearestRoute.getDistance();
				newStart = index;
			}
			strategy.setDistance(distance);
		}
		Collections.sort(allRoutes);
		DeliveryStrategy strategy = allRoutes.get(0);
		System.out.println("总路程：" + strategy.getDistance());
		System.out.println(strategy);
	}

}

项目完整代码下载地址：https://download.csdn.net/download/pengjunlee/10713984