【算法】公司食堂-美团2021校招笔试

【算法】公司食堂-美团2021校招笔试

https://www.nowcoder.com/questionTerminal/601815bea5544f389bcd20fb5ebca6a8

1.题目

2.我的解法（没有AC，运行超时）

• 代码

  package 公司食堂;
  
  
  import java.io.*;
  
  /*
  根据排队人的性别，从左到右判断是否优先做这个餐桌
  遍历一轮没有优先桌，再遍历一遍选择次优
   */
  public class CompanyCanteen {
  
  
      public static void companyCanteen(int[] peopleDispose, int M, char[] sexInQueue, int[] willGo) {
          int empty = 0;//空桌
          int onePeople = 0;//一人桌
          for (int i = 0; i < M; i++) {
              empty = 0;
              onePeople = 0;
              //标记空桌和一人桌
              //涉及第几桌要+1（因为从1开始）
              for (int j = 0; j < peopleDispose.length; j++) {
                  if (onePeople == 0 && peopleDispose[j] == 1)
                      onePeople = j + 1;
  
                  if (empty == 0 && peopleDispose[j] == 0)
                      empty = j + 1;
  
                  if (onePeople != 0 && empty != 0)
                      break;
              }
              //判断男性和女性的结果,更新当前餐桌的人数
              /*
              男性没有1人桌了，才去空桌
              女性没有空桌了，才去一人桌
               */
              if (sexInQueue[i] == 'M') {
                  if (onePeople == 0) {
                      willGo[i] = empty;
                      peopleDispose[empty - 1]++;
                  } else {
                      willGo[i] = onePeople;
                      peopleDispose[onePeople - 1]++;
                  }
              } else {
                  if (empty == 0) {
                      willGo[i] = onePeople;
                      peopleDispose[onePeople - 1]++;
                  } else {
                      willGo[i] = empty;
                      peopleDispose[empty - 1]++;
                  }
              }
          }
      }
  
      public static void main(String[] args) throws IOException {
          BufferedReader reader = new BufferedReader(new InputStreamReader(System.in));
          BufferedWriter writer = new BufferedWriter(new OutputStreamWriter(System.out));
  
  
          int T = Integer.parseInt(reader.readLine());//数据组数
          int N;//餐桌个数
          int[] peopleDispose;//人数在餐桌上的排布
          int M;//排队人数
          char[] sexInQueue;//在排队的人的性别
          int[] willGo;//预测结果
  
          //每组数据占4行
          for (int i = 0; i < T; i++) {
              N = Integer.parseInt(reader.readLine());
  
              peopleDispose = new int[N];
              String disposeStr = reader.readLine();
              for (int j = 0; j < disposeStr.length(); j++) {
                  //字符转数字时注意Ascll码
                  peopleDispose[j] = disposeStr.charAt(j) - '0';
              }
  
              M = Integer.parseInt(reader.readLine());
  
              sexInQueue = new char[M];
              String sexInQueueStr = reader.readLine();
              for (int j = 0; j < sexInQueueStr.length(); j++) {
                  sexInQueue[j] = sexInQueueStr.charAt(j);
              }
  
              willGo = new int[M];
  
              companyCanteen(peopleDispose, M, sexInQueue, willGo);
              for (int k = 0; k < willGo.length; k++) {
                  writer.write(Integer.toString(willGo[k]));//输出必须是String类型的
                  writer.newLine();
              }
  
              writer.flush();
          }
      }
  }
  

不好在哪里

• 时间复杂度太高，把System输入输出改用BufferedReader和BufferedWriter也超时。每次循环都要找最左边的空桌和一人桌，大可不必，可以利用数据结构使其简便。

2.推荐解法：优先队列

• 代码

  package 公司食堂;
  
  import java.io.*;
  import java.util.ArrayList;
  import java.util.List;
  import java.util.PriorityQueue;
  
  /**
   * @author musecho801
   * @title CompanyCanteen1
   * @description 遍历桌号，将所有空桌、一人桌分别入队两个优先队列，
   * 根据性别判断会去哪个桌号
   * @date 2021/3/11 17:21
   */
  public class CompanyCanteen1 {
  
      public void companyCanteen(String peopleDisposeStr, int M, String sexStr, int[] rs) {
          List<PriorityQueue> list = new ArrayList<>(2);
          PriorityQueue<Integer> emptyPQ = new PriorityQueue<>();
          PriorityQueue<Integer> oneTablePQ = new PriorityQueue<>();
          list.add(emptyPQ);
          list.add(oneTablePQ);
          int k = 0;//控制rs的下标
  
          //得到空桌、一人桌 两个优先队列(默认升序)
          //i为 桌号-1
          for (int i = 0; i < peopleDisposeStr.length(); i++) {
              if (peopleDisposeStr.charAt(i) == '0') {
                  emptyPQ.add(i);
              } else if (peopleDisposeStr.charAt(i) == '1') {
                  oneTablePQ.add(i);
              }
          }
  
          //根据性别判断会去哪个桌号
          for (int i = 0; i < sexStr.length(); i++) {
              //男性：只有没有一人桌时，才选择空桌
              if (sexStr.charAt(i) == 'M') {
                  if (oneTablePQ.peek() != null) {
                      rs[k++] = oneTablePQ.poll();
                  } else {
                      oneTablePQ.add(emptyPQ.peek());
                      rs[k++] = emptyPQ.poll();
                  }
              } else if (sexStr.charAt(i) == 'F') {//女性：只有没有空桌时，才选择一人桌
                  if (emptyPQ.peek() != null) {
                      oneTablePQ.add(emptyPQ.peek());
                      rs[k++] = emptyPQ.poll();
                  } else {
                      rs[k++] = oneTablePQ.poll();
                  }
              }
          }
  
          //注意：rs为去第i桌，值要+1
          for (int i = 0; i < M; i++)
              rs[i]++;
      }
  
      public static void main(String[] args) throws IOException {
          CompanyCanteen1 cc = new CompanyCanteen1();
          BufferedReader reader = new BufferedReader(new InputStreamReader(System.in));
          BufferedWriter writer = new BufferedWriter(new OutputStreamWriter(System.out));
  
          int T = Integer.parseInt(reader.readLine());//数据组数
          for (int i = 0; i < T; i++) {
              int N = Integer.parseInt(reader.readLine());//餐桌个数
              String peopleDisposeStr = reader.readLine();//餐桌人数分布
              int M = Integer.parseInt(reader.readLine());//排队人数
              String sexStr = reader.readLine();//排队人的性别
              int[] rs = new int[M];//结果
  
              cc.companyCanteen(peopleDisposeStr, M, sexStr, rs);
              for (int t : rs) {
                  writer.write(Integer.toString(t));
                  writer.newLine();
              }
              //flush()冲刷出流，将所有缓冲数据强制发送至目的地。不加这个，是无法输出的
              writer.flush();
          }
  
      }
  }
  

亮点

• 使用优先队列直接存储所有空桌、一人桌
• BufferedReader和BufferedWriter的运行速度较快，学会使用

参考

推荐算法参考：https://blog.nowcoder.net/n/933a93eea0194ebdab05bb464497a0b4