Question

我们有两个名单，让我们说学生和他们的分数。我想比较这两个列表并找到新列表和旧列表之间的增量，然后找到插入或更新到新列表中的任何更改的最少侵入性方法。解决这个问题的最佳算法是什么？希望专注于对新列表和性能的最小量更改。

示例代码：

List<ListItem> existingList = new List<ListItem>();
List<ListItem> newList = new List<ListItem>();

public TopLists()
{
  InitTwoLists();
}

private void InitTwoLists()
{
  existingList.Add(new ListItem { Name = "Shane", Score = 100 });
  existingList.Add(new ListItem { Name = "Mark", Score = 95 });
  existingList.Add(new ListItem { Name = "Shane", Score = 94 });
  existingList.Add(new ListItem { Name = "Steve", Score = 90 });
  existingList.Add(new ListItem { Name = "Brian", Score = 85 });
  existingList.Add(new ListItem { Name = "Craig", Score = 85 });
  existingList.Add(new ListItem { Name = "John", Score = 82 });
  existingList.Add(new ListItem { Name = "Steve", Score = 81 });
  existingList.Add(new ListItem { Name = "Philip", Score = 79 });
  existingList.Add(new ListItem { Name = "Peter", Score = 70 });

  newList.Add(new ListItem { Name = "Shane", Score = 100 });
  newList.Add(new ListItem { Name = "Steve", Score = 96 });  // This is change
  newList.Add(new ListItem { Name = "Mark", Score = 95 });
  newList.Add(new ListItem { Name = "Shane", Score = 94 });
  newList.Add(new ListItem { Name = "Brian", Score = 85 });
  newList.Add(new ListItem { Name = "Craig", Score = 85 });
  newList.Add(new ListItem { Name = "John", Score = 82 });
  newList.Add(new ListItem { Name = "Steve", Score = 81 });
  newList.Add(new ListItem { Name = "Philip", Score = 79 });
  newList.Add(new ListItem { Name = "Peter", Score = 70 });
}
}

public void CompareLists()
{
  // How would I find the deltas and update the new list with any changes from old?
}
}

public class ListItem
{
  public string Name { get; set; }
  public int Score { get; set; }
}

**编辑：期望输出***

所需的输出是实际更改带有增量的newList。例如，在这种情况下：

newList.Add(new ListItem { Name = "Shane", Score = 100 });
  newList.Add(new ListItem { Name = "Steve", Score = 96 });  // This is change
  newList.Add(new ListItem { Name = "Mark", Score = 95 });
  newList.Add(new ListItem { Name = "Shane", Score = 94 });
  newList.Add(new ListItem { Name = "Brian", Score = 85 });
  newList.Add(new ListItem { Name = "Craig", Score = 85 });
  newList.Add(new ListItem { Name = "John", Score = 82 });
  newList.Add(new ListItem { Name = "Steve", Score = 81 });
  newList.Add(new ListItem { Name = "Roger", Score = 80 });  // Roger is a new entry
  newList.Add(new ListItem { Name = "Phillip", Score = 79 });  // Philip moved down one

//彼得以70分的成绩从这份名单中脱颖而出，因为我只想要前10名。

所以改变是：

更新“史蒂夫”的记录2，分数已经改变在第9位插入新唱片“Roger” 将“彼得”的记录从前10名中删除。

Answer 1

你能使用Linq：

List<ListItem> list1 = GetYourList1();
List<ListItem> list2 = GetYourList2();
var diff = list1.Except(list2);

您的具体示例：

var diff = newList.Except(existingList);

不确定它是否最有效，但它很简洁：）

Answer 2

如果您正在寻找一种与语言无关的通用解决方案，那么您正在寻找某种有序列表data synchronization。基本算法是：

i1 = 0
i2 = 0
while (i1 < list1.size && i2 < list2.size)
{
  if (list1[i1] < list2[i2])
  {
    //list1[i1] is not in list2
    i1++
  }
  else if (list1[i1] > list2[i2])
  {
    //list2[i2] is not in list1
    i2++
  }
  else
  {
    //item is in both lists
    i1++
    i2++
  }
}
if (i1 < list1.size)
   //all remaining list1 items are not in list2
if (i2 < list2.size)
   //all remaining list2 items are not in list1

Answer 3

如果列表中没有两次相同的名称，这应该能够解决问题。在你的例子中，你有2x Steve，但你需要一种方法来区分它们。

public static List<ListItem> CompareLists(List<ListItem> existingList, List<ListItem> newList)
{
    List<ListItem> mergedList = new List<ListItem>();
    mergedList.AddRange(newList);
    mergedList.AddRange(existingList.Except(newList, new ListItemComparer()));
    return mergedList.OrderByDescending(x => x.Score).Take(10).ToList();
}

public class ListItemComparer : IEqualityComparer<ListItem>
{
    public bool Equals(ListItem x, ListItem y)
    {
        return x.Name == y.Name;
    }

    public int GetHashCode(ListItem obj)
    {
        return obj.Name.GetHashCode();
    }
}

您可以这样称呼它：

newList = CompareLists(existingList, newList);

比较两个列表并找到这两个列表之间的差异的最有效模式/算法是什么？

3 个答案: