在C＃中，如何按指定的位数向右旋转列表？ [英] In C#, how do I rotate a list to the right by the specified number of places?

问题描述

我特别给出了这行代码：

I'm given this line of code in particular:

public void Test8(List<int> items, int places)

这个问题的任务是提出解决方案，我可以通过指定的位数向右旋转List。 List旋转可以看作是圆形，这意味着末尾的元素会回绕到开头，反之亦然。



我该怎么做正确的方法？是否有多种方法可以手动执行此操作而不使用任何类型的花式代码？



示例：

The tasks for this problem is to come up with solution where I am able to rotate the List to the right by the specified number of places. A List rotation can be seen as circular, which means the elements that fall of the end would wrap around to the beginning, and vice versa.

How can I do this the correct way? Is there multiple ways to do this manually without using any sort fancy code?

Example:

Initial Array or List: 20, 30, 40, 50,60, 70
Rotated to the right by 3 places: 50, 60, 70, 20, 30, 40.

我尝试过：

What I have tried:

public void Test8(List<int> items, int places)
{
    int rotate = places;
    int[] results = new int[items.Count];

    for (int i = 0; i < items.Count; i++)
    {
        results[i] = items[(i + rotate) % items.Count];
    }
}

推荐答案

试试这个：

Try this:

public void Test8(List<int> items, int places)
{ 
    int nItem;

    for (int i = 0; i < places; i++)
    {
        nItem = items[items.Count - 1];     // get the last item of the list
        items.RemoveItem(items.Count - 1);  // remove this item from the end  ...
        items.InsertItem(0, nItem);         // ... and insert this (last) item in front of the list
    }
}

你基本上有2种技巧

- 旋转并复制到新列表

- 旋转到位



旋转副本是解决方案1的技巧。

要计算元素的新位置，你有应用公式：

NewPosition =（OldPosition + Rotation）％SizeOfList



轮换到位

仅轮换1和-1是实用的。您只需根据需要重复多次。

- 伪代码

You have basically 2 techniques
- Rotation with copy to a new list
- Rotation in place

Rotation with copy is the technique of solution 1.
To calc to new positionof an element, you have to apply the formula:
NewPosition= (OldPosition+ Rotation) % SizeOfList

Rotation in place
Only rotation of 1 and -1 are practical. You just have to repeat as many times as needed.
- pseudo code

if (rotation== -1)
{
    tmp= list[0]
    for scan= 1; scan < list.count; scan++)
    {
        list[scan-1]= list[scan];
    }
    list[list.count-1]= tmp;
}
else
{
    tmp= list[list.count-1]
    for scan= list.count-1; scan >=0; scan--)
    {
        list[scan]= list[scan-1];
    }
    list[0]= tmp;
}

解决方案1的稍微高效的版本：

A slightly more efficient version of Solution 1:

public void Test8(List<int> items, int places)
{
    // Handle cases where the number of places is greater than or equal to the number of items:
    places %= items.Count;
    if (places == 0) return;
    
    int[] range = new int[places];
    items.CopyTo(items.Count - places, range, 0, places);
    items.RemoveRange(items.Count - places, places);
    items.InsertRange(0, range);
}

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