exercise5_20.java

java程序设计导论（daniel liang著） 所有偶数课后习题答案

public class Exercise5_20 {
  public static void main(String args[]) {
    // Students' answers to the questions
    char[][] answers = {
      {'A', 'B', 'A', 'C', 'C', 'D', 'E', 'E', 'A', 'D'},
      {'D', 'B', 'A', 'B', 'C', 'A', 'E', 'E', 'A', 'D'},
      {'E', 'D', 'D', 'A', 'C', 'B', 'E', 'E', 'A', 'D'},
      {'C', 'B', 'A', 'E', 'D', 'C', 'E', 'E', 'A', 'D'},
      {'A', 'B', 'D', 'C', 'C', 'D', 'E', 'E', 'A', 'D'},
      {'B', 'B', 'E', 'C', 'C', 'D', 'E', 'E', 'A', 'D'},
      {'B', 'B', 'A', 'C', 'C', 'D', 'E', 'E', 'A', 'D'},
      {'E', 'B', 'E', 'C', 'C', 'D', 'E', 'E', 'A', 'D'}};

    // Key to the questions
    char[] keys = {'D', 'B', 'D', 'C', 'C', 'D', 'A', 'E', 'A', 'D'};
    int[] correctCounts = new int[answers.length];

    // Grade all answers
    for (int i = 0; i < answers.length; i++) {
      // Grade one student
      for (int j = 0; j < answers[i].length; j++) {
        if (answers[i][j] == keys[j])
          correctCounts[i]++;
      }
    }

    int[] indexList = new int[answers.length];

    // Sort totalScores
    sortAndKeepIndex(correctCounts, indexList);

    // Display result
    for (int i = 0; i < correctCounts.length; i++)
      System.out.println("Student " + indexList[i] + ": " +
        correctCounts[i]);

    System.out.println("Mean is " + Deviation.mean(correctCounts));
    System.out.println("Deviation is " + Deviation.deviation(correctCounts));
  }

  /** The method for sorting the numbers */
  static void sortAndKeepIndex(int[] list, int[] indexList) {
    int currentMax;
    int currentMaxIndex;

    // Initialize indexList
    for (int i = 0; i < indexList.length; i++)
      indexList[i] = i;

    for (int i = list.length - 1; i >= 1; i--) {
      // Find the maximum in the list[0..i]
      currentMax = list[i];
      currentMaxIndex = i;

      for (int j = i - 1; j >= 0; j--) {
        if (currentMax < list[j]) {
          currentMax = list[j];
          currentMaxIndex = j;
        }
      }

      // Swap list[i] with list[currentMaxIndex] if necessary;
      if (currentMaxIndex != i) {
        list[currentMaxIndex] = list[i];
        list[i] = currentMax;

        // Swap the index in indexList too
        int temp = indexList[i];
        indexList[i] = indexList[currentMaxIndex];
        indexList[currentMaxIndex] = temp;
      }
    }
  }
}