Week7

请背诵四道FRQ（见PDF）的solution，并回答关于代码的相应问题（下面有例子）。理解代码很重要。

Digits

public Digits(int num) {
    digitList = new ArrayList<Integer>();
    if (num == 0) {
        digitList.add(0);
    }
    else {
        int n = num;
        while (n > 0) {
            digitList.add(0, n%10);
            n /= 10;
        }
    }
}

public boolean isStrictlyIncreasing() {
    for (int i = 0; i < digitList.size() - 1; i++) {
        if (digitList.get(i) >= digitList.get(i + 1)) {
            return false;
        }
    }
    return true;

可能会问到的问题包括但不仅限于：

第二问中i的取值范围为什么是digitList.size()-1?
第一问中为什么要检查num==0？不检查可以吗？

下面题目的问题类似。

MemberInfo

public void addMembers(String[] names, int gradYear) {
  for(String name: names) {
    MemberInfo newMem = new MemberInfo(name, gradYear, true);
    memberList.add(newMem);
}

public ArrayList<MemberInfo> removeMembers(int year)
{
  ArrayList<MemberInfo> goodStanding = new ArrayList<MemberInfo>(); 

  int i = 0;
  while(i < memberList.size())
  {
    if(memberList.get(i).getGradYear() <= year)
    {
      MemberInfo removed = memberList.remove(i);
      if(removed.inGoodStanding())
        goodStanding.add(removed);
    }
    else
      i++;
  }
  return goodStanding;
}

ArrayResizer

public static boolean isNonZeroRow(int[][] array2D, int r)
{
  for(int c = 0; c < array2D[0].length; c++) {
    if(array2D[r][c] == 0)
      return false;
  }
  return true;
}

public static int[][] resize(int[][] array2D)
{
  int[][] newArray = new int[numNonZeroRows(array2D)][array2D[0].length];
  int newR = 0;
  for(int oldR = 0; oldR < array2D.length; oldR++)
  {
    if(isNonZeroRow(array2D, oldR))
    {
      // could copy elements within row instead
      newArray[newR] = array2D[oldR];
      newR++;
    }
  } 
 return newArray;
}

ArrayTester

public static int[] getColumn(int[][] arr2D, int c)
{
  int[] column = new int[arr2D.length];

  for(int i = 0; i < column.length; i++)
    column[i] = arr2D[i][c];

  return column;
}

public static boolean isLatin(int[][] square)
{
  if(containsDuplicates(square[0]))
    return false;

  for(int r = 1; r < square.length; r++)
    if(!hasAllValues(square[0], square[r]) )
      return false;

  for(int c = 0; c < square[0].length; c++)
    if(!hasAllValues(square[0], getColumn(square, c)))
      return false;

  return true;
}

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public Digits(int num) { digitList = new ArrayList<Integer>(); if (num == 0) { digitList.add(0); } else { int n = num; while (n > 0) { digitList.add(0, n%10); n /= 10; } } }

public boolean isStrictlyIncreasing() { for (int i = 0; i < digitList.size() - 1; i++) { if (digitList.get(i) >= digitList.get(i + 1)) { return false; } } return true;

public ArrayList<MemberInfo> removeMembers(int year) { ArrayList<MemberInfo> goodStanding = new ArrayList<MemberInfo>(); int i = 0; while(i < memberList.size()) { if(memberList.get(i).getGradYear() <= year) { MemberInfo removed = memberList.remove(i); if(removed.inGoodStanding()) goodStanding.add(removed); } else i++; } return goodStanding; }

public static int[][] resize(int[][] array2D) { int[][] newArray = new int[numNonZeroRows(array2D)][array2D[0].length]; int newR = 0; for(int oldR = 0; oldR < array2D.length; oldR++) { if(isNonZeroRow(array2D, oldR)) { // could copy elements within row instead newArray[newR] = array2D[oldR]; newR++; } } return newArray; }

public static boolean isLatin(int[][] square) { if(containsDuplicates(square[0])) return false; for(int r = 1; r < square.length; r++) if(!hasAllValues(square[0], square[r]) ) return false; for(int c = 0; c < square[0].length; c++) if(!hasAllValues(square[0], getColumn(square, c))) return false; return true; }