Java实现筛选全成绩高于阈值的学生名单问题求助

需要实现逻辑：返回所有成绩均严格高于特定阈值的学生姓名列表，尝试嵌套if和while循环后仍无法正确实现，现有代码要么错误包含低于阈值的学生，要么把所有学生都加入列表。

原实现代码 #

import java.util.LinkedList;
import java.util.List;
import java.util.Map;

public class ExampleMap {

  /**
   * Return a list of "high scoring" students --- High scoring students are
   * students who have all grades strictly greater than the given threshold.
   *
   * @param scoresByApplicantName A map of applicant names to applicant scores
   * @param scoreThreshold        The score threshold
   * @return The list of high-scoring applicant names
   */
  public static List<String> highScoringStudents(Map<String, List<CourseGrade>> scoresByApplicantName, int scoreThreshold) {

    List<String> highScoringStudents = new LinkedList<>();

    /*
     * Build a list of the names of applicants who have scores strictly greater than
     * the given threshold.
     */
    for (Map.Entry<String, List<CourseGrade>> current : scoresByApplicantName.entrySet()) {
      List<CourseGrade> course_grades = current.getValue();
      for (CourseGrade courses : course_grades) {
        if (courses.getScore() > scoreThreshold) {
          highScoringStudents.add(current.getKey());
        }
      }
    }
    return highScoringStudents;
  }
}

CourseGrade类代码（无需修改） #

/*
 * This file should remain unchanged.
 */
public class CourseGrade {
  private String courseName;
  private int score; 

  /**
   * This is a constructor. It creates a new CourseGrade with the specified scores.
   * @param courseName
   * @param score 
   */
  public CourseGrade(String courseName, int score) {
    this.courseName = courseName;
    this.score = score;
  }

  public String getCourseName() {
    return this.courseName;
  }

  public int getScore() {
    return this.score;
  }
}

测试用例 #

@Test
public void testExampleMap1()
{
   Map<String, List<CourseGrade>> courseListsByStudent = new HashMap<>();
   courseListsByStudent.put("Julie",
      Arrays.asList(
         new CourseGrade("CPE 123", 89),
         new CourseGrade("CPE 101", 90),
         new CourseGrade("CPE 202", 99),
         new CourseGrade("CPE 203", 100),
         new CourseGrade("CPE 225", 89)));
   courseListsByStudent.put("Paul",
      Arrays.asList(
         new CourseGrade("CPE 101", 86),
         new CourseGrade("CPE 202", 80),
         new CourseGrade("CPE 203", 76),
         new CourseGrade("CPE 225", 80)));
   courseListsByStudent.put("Zoe",
      Arrays.asList(
         new CourseGrade("CPE 123", 99),
         new CourseGrade("CPE 203", 91),
         new CourseGrade("CPE 471", 86),
         new CourseGrade("CPE 473", 90),
         new CourseGrade("CPE 476", 99),
         new CourseGrade("CPE 572", 100)));

   List<String> expected = Arrays.asList("Julie", "Zoe");

   /*
    * Why compare HashSets here?  Just so that the order of the
    * elements in the list is not important for this test.
    */
   assertEquals(new HashSet<>(expected),
      new HashSet<>(ExampleMap.highScoringStudents(
         courseListsByStudent, 85)));
}

错误原因分析 #

原代码逻辑完全偏离需求：只要学生有一门课程成绩高于阈值，就会把该学生姓名重复加入结果列表（有几门达标就加几次），但实际需要的是所有课程成绩都严格高于阈值的学生才符合条件。

修正后的代码 #

import java.util.LinkedList;
import java.util.List;
import java.util.Map;

public class ExampleMap {

  /**
   * Return a list of "high scoring" students --- High scoring students are
   * students who have all grades strictly greater than the given threshold.
   *
   * @param scoresByApplicantName A map of applicant names to applicant scores
   * @param scoreThreshold        The score threshold
   * @return The list of high-scoring applicant names
   */
  public static List<String> highScoringStudents(Map<String, List<CourseGrade>> scoresByApplicantName, int scoreThreshold) {

    List<String> highScoringStudents = new LinkedList<>();

    for (Map.Entry<String, List<CourseGrade>> current : scoresByApplicantName.entrySet()) {
      List<CourseGrade> courseGrades = current.getValue();
      // 先默认该学生所有成绩达标
      boolean allScoresAboveThreshold = true;
      for (CourseGrade courseGrade : courseGrades) {
        // 只要有一门成绩不达标，立即标记为不符合并终止循环
        if (courseGrade.getScore() <= scoreThreshold) {
          allScoresAboveThreshold = false;
          break;
        }
      }
      // 确认所有成绩都达标后，再加入结果列表
      if (allScoresAboveThreshold) {
        highScoringStudents.add(current.getKey());
      }
    }
    return highScoringStudents;
  }
}

修正逻辑说明 #

1. 对每个学生初始化标记位，默认其所有成绩达标
2. 遍历学生的课程成绩，一旦发现某门成绩≤阈值，立即修改标记位并跳出循环（减少不必要的遍历）
3. 遍历结束后，仅当标记位仍为true时，将学生姓名加入结果列表

该逻辑完全匹配需求，同时避免了重复添加的问题，能通过给定的测试用例。

内容的提问来源于stack exchange，提问作者awoobis