华为OJ之自动售货系统

本题主要难点有两部分：

1，找零算法。如何找零应该是最具技巧性的部分，根据已有的硬币金额分布，对应的解决办法可能会有不同。本题中的1，2，5，10这种情况满足贪心性质，故我们简单的用贪心算法的思想来解决。一般更加通用的是利用动态规划或者穷举，这个后面有机会会专门进行讨论。

2，代码业务逻辑。本题所描述的系统已经是一个较为完整的贩卖系统，更多地需要我们从整体上把握代码结构，明白个部分间的关系。如果初始感到无从下手，那么说明在较复杂情况下的编程能力还有欠缺，日后应继续练习。

由于临近入职比较忙，这里简单附上所有的源码，参考其中的注释应不难理解。

 import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.HashMap;
 import java.util.Scanner;
 import java.util.Stack;

 public class VendingSystem {

     static ArrayList<Product> products;//商品信息
     static ArrayList<Coin> coins;//币盒信息
     static int balance;//余额

     public static void main(String[] args) {
         String orders = getParas();
         String[] orderArray = orders.split(";");
         handleOrder(orderArray);
     }

     /*
      * 处理接收到的命令
      */
     public static void handleOrder(String[] orderArray) {
         char operation = ' ';
         for (String order : orderArray) {
             operation = order.charAt(0);
             switch (operation) {
             //初始化
             case 'r':
                 initialize(order);
                 break;
             //投币
             case 'p':
                 dropCoin(order);
                 break;
             //购买
             case 'b':
                 buy(order);
                 break;
             //退币
             case 'c':
                 change(order);
                 break;
             //查询
             case 'q':
                 query(order);
                 break;
             default:
                 break;
             }
         }
     }

     /*
      * 获取输入命令
      */
     public static String getParas() {
         Scanner reader = new Scanner(System.in);
         String orders = reader.nextLine();
         reader.close();
         return orders;
     }

     /*
      * 初始化商品个数和钱币个数
      */
     public static void initialize(String paras) {
         int[] productPrice = {2, 3, 4, 5, 8, 6};
         int[] coinValue = {1, 2, 5, 10};
         String[] initializationData = paras.split(" ");
         products = new ArrayList<Product>();
         coins = new ArrayList<Coin>();
         String[] productNum = initializationData[1].split("-");
         for (int i = 0; i < productNum.length; i ++) {
             products.add(new Product(("A" + (i + 1)), productPrice[i], Integer.parseInt(productNum[i])));
         }
         String[] coinNum = initializationData[2].split("-");
         for (int j = 0; j < coinNum.length; j ++) {
             coins.add(new Coin((coinValue[j] + " yuan coin"), coinValue[j], Integer.parseInt(coinNum[j])));
         }
         System.out.println("S001:Initialization is successful");
     }

     /*
      * 处理查询请求
      */
     public static void query(String order) {
         String[] queryPara = order.split(" ");
         if (queryPara.length < 2 || (!queryPara[1].equals("0") && !queryPara[1].equals("1"))) {
             System.out.println("E010:Parameter error");
             return;
         }
         if (queryPara[1].equals("0")) {
             int weight = 0;//weight用来保存每件商品的排序优先级，越大则优先级越高,注意weight是不会重复的
             HashMap<Integer, Integer> weightAndIndexMap = new HashMap<Integer, Integer>();
             int[] weights = new int[products.size()];
             for (int i = 0; i < products.size(); i ++) {
                 weight = products.get(i).getNum() * 10 - i;
                 weights[i] = weight;
                 weightAndIndexMap.put(weight, i);
             }
             Arrays.sort(weights);
             Product tempProduct = null;
             for (int i = weights.length - 1; i >= 0; i --) {
                 tempProduct = products.get(weightAndIndexMap.get(weights[i]));
                 System.out.println(tempProduct.getName() + " " + tempProduct.getPrice() + " " + tempProduct.getNum());
             }

         } else {
             for (Coin coin : coins) {
                 System.out.println(coin.name + " number=" + coin.num);
             }
         }
     }

     /*
      * 处理投币
      */
     public static void dropCoin(String order) {
         String[] dropPara = order.split(" ");
         //注意题目给的稍微有点问题，这里的判断确认参数为正整数
         //投币金额
         int dropValue = Integer.parseInt(dropPara[1]);
         if (dropValue != 1 && dropValue != 2 && dropValue != 5 && dropValue != 10 && dropValue < 10) {
             System.out.println("E002:Denomination error");
         } else {
             //钱盒中1, 2硬币总额
             int temp = coins.get(0).getNum() * coins.get(0).getValue() +
                     coins.get(1).getNum() * coins.get(1).getValue();
             if (temp < dropValue && dropValue != 1 && dropValue != 2) {
                 System.out.println("E003:Change is not enough, pay fail");
                 return;
             }
             if (Integer.parseInt(dropPara[1]) > 10) {
                 System.out.println("E004:Pay the balance is beyond the scope biggest");
                 return;
             }
             boolean isProductEmpty = true;
             for (Product product : products) {
                 if (product.getNum() > 0) {
                     isProductEmpty = false;
                     break;
                 }
             }
             if (isProductEmpty) {
                 System.out.println("E005:All the goods sold out");
                 return;
             }

             switch (dropValue) {
             case 1:
                 coins.get(0).setNum(coins.get(0).getNum() + 1);
                 break;
             case 2:
                 coins.get(1).setNum(coins.get(1).getNum() + 1);
                 break;
             case 5:
                 coins.get(2).setNum(coins.get(2).getNum() + 1);
                 break;
             case 10:
                 coins.get(3).setNum(coins.get(3).getNum() + 1);
                 break;
             default:
                 break;
             }
             balance += dropValue;
             System.out.println("S002:Pay success,balance=" + balance);
         }
     }

     /*
      * 处理购买命令
      */
     public static void buy(String order) {
         String[] buyPara = order.split(" ");
         HashMap<String, Integer> productNameAndIndexMap = new HashMap<String, Integer>();
         for (int i = 0; i < products.size(); i ++) {
             productNameAndIndexMap.put(products.get(i).getName(), i);
         }
         String productToBuy = buyPara[1];
         if (productToBuy.equals("A1") || productToBuy.equals("A2") ||
                 productToBuy.equals("A3") ||productToBuy.equals("A4") ||
                 productToBuy.equals("A5") ||productToBuy.equals("A6")) {
             Product tempProduct = products.get(productNameAndIndexMap.get(productToBuy));
             if (tempProduct.getNum() == 0) {
                 System.out.println("E007:The goods sold out");
                 return;
             }
             if (tempProduct.getPrice() > balance) {
                 System.out.println("E008:Lack of balance");
                 return;
             }
             tempProduct.setNum(tempProduct.getNum() - 1);
             balance -= tempProduct.getPrice();
             System.out.println("S003:Buy success,balance=" + balance);
         } else {
             System.out.println("E006:Goods does not exist");
         }
     }

     /*
      * 退钱找零
      */
     public static void change(String order) {
         if (balance == 0) {
             System.out.println("E009:Work failure");
             return;
         }
         int[] coinNums = new int[coins.size()];
         for (int i = 0; i < coins.size(); i ++) {
             coinNums[i] = coins.get(i).getNum();
         }
         findChange(coinNums, balance);
     }

     /*
      * 退币方法
      */
     public static boolean findChange(int[] coinNums, int countToChange) {
         if (countToChange < 1) {
             return false;
         }
         int originalCount = countToChange;
         boolean isFound = false;
         Stack<Integer> coinStack = new Stack<Integer>();
         Stack<Integer> changeStack = new Stack<Integer>();
         for (int i = 0; i < coinNums.length; i ++) {
             for (int j = 0; j < coinNums.length - i; j ++) {
                 for (int k = 0; k < coinNums[j]; k ++) {
                     switch (j) {
                     case 0:
                         coinStack.push(1);
                         break;
                     case 1:
                         coinStack.push(2);
                         break;
                     case 2:
                         coinStack.push(5);
                         break;
                     case 3:
                         coinStack.push(10);
                         break;
                     default:
                         break;
                     }
                 }
             }
             while (!coinStack.isEmpty()) {
                 int tempCoinValue = coinStack.pop();
                 if (countToChange >= tempCoinValue) {
                     countToChange -= tempCoinValue;
                     changeStack.push(tempCoinValue);
                 }
             }
             if (countToChange == 0) {
                 isFound = true;
                 break;
             } else {
                 countToChange = originalCount;
                 coinStack.clear();
                 changeStack.clear();
             }
         }
         if (isFound) {
             balance = 0;
             int[] changeResult = new int[coinNums.length];
             while (!changeStack.isEmpty()) {
                 switch (changeStack.pop()) {
                 case 1:
                     changeResult[0] ++;
                     break;
                 case 2:
                     changeResult[1] ++;
                     break;
                 case 5:
                     changeResult[2] ++;
                     break;
                 case 10:
                     changeResult[3] ++;
                     break;
                 default:
                     break;
                 }
             }
             for (int i = 0; i < changeResult.length; i ++) {
                 coins.get(i).setNum(coins.get(i).getNum() - changeResult[i]);
                 switch (i) {
                 case 0:
                     System.out.println("1 yuan coin number=" + changeResult[i]);
                     break;
                 case 1:
                     System.out.println("2 yuan coin number=" + changeResult[i]);
                     break;
                 case 2:
                     System.out.println("5 yuan coin number=" + changeResult[i]);
                     break;
                 case 3:
                     System.out.println("10 yuan coin number=" + changeResult[i]);
                     break;
                 default:
                     break;
                 }
             }
             return true;
         } else {
             return findChange(coinNums, originalCount - 1);
         }
     }
 }
 class Product {

     String name;
     int price;
     int num;

     public String getName() {
         return name;
     }
     public void setName(String name) {
         this.name = name;
     }
     public int getPrice() {
         return price;
     }
     public void setPrice(int price) {
         this.price = price;
     }
     public int getNum() {
         return num;
     }
     public void setNum(int num) {
         this.num = num;
     }

     public Product() {

     }

     public Product(String name, int price, int num) {
         super();
         this.name = name;
         this.price = price;
         this.num = num;
     }
     @Override
     public String toString() {
         return "Product [name=" + name + ", price=" + price + ", num=" + num + "]";
     }

 }
 class Coin {

     String name;
     int value;
     int num;

     public String getName() {
         return name;
     }
     public void setName(String name) {
         this.name = name;
     }
     public int getValue() {
         return value;
     }
     public void setValue(int value) {
         this.value = value;
     }
     public int getNum() {
         return num;
     }
     public void setNum(int num) {
         this.num = num;
     }
     public Coin() {
         super();
     }
     public Coin(String name, int value, int num) {
         super();
         this.name = name;
         this.value = value;
         this.num = num;
     }
     @Override
     public String toString() {
         return "Coin [name=" + name + ", value=" + value + ", num=" + num + "]";
     }

 }