Question

我们的老师要求我们实施课程LinkedList。我能够实现他要求的一切。但他给了我们一个我无法解决的奖金问题。

他要求我们实施这个功能：

public void add(float x, int pos)
{
  // Add x at the position pos, pos = 0 refer to the first element.
}

他还要求他的代码验证以下UnitTest：

public class UnitTest1
{
    private MyList l;

    public UnitTest1()
    {
        l = new MyList();
        for (int i = 0; i < 10; ++i)
        {
            l.add(i * i);
        }
        for (int i = 0; i < 10; ++i)
        {
            l.add(i * i);
        }
    }

    [TestMethod]
    public void TestAdd()
    {
        Assert.AreEqual(l.count(), 20);
    }
    [TestMethod]
    public void TestGet()
    {
        for (int i = 0; i < 10; ++i)
        {
            Assert.AreEqual(l.get(i), (9 - i) * (9 - i));
        }
        for (int i = 10; i < 20; ++i)
        {
            Assert.AreEqual(l.get(i), (19 - i) * (19 - i));
        }
    }
    [TestMethod]
    public void TestFind()
    {
        int k;
        for (int i = 0; i < 100; ++i)
        {
            for (k = 0; k < 10; ++k)
            {
                if (k * k == i)
                {
                    Assert.AreEqual(l.find(i), true);
                    break;
                }
            }
            if (k == 10)
            {
                Assert.AreEqual(l.find(i), false);
            }
        }
    }

    [TestMethod]
    public void TestStats()
    {
        Assert.AreEqual(l.max(), 81);
        float s = 0;
        for (int i = 0; i < 10; ++i)
        {
            s += i * i + i * i;
        }
        Assert.AreEqual(l.sum(), s);
        Assert.AreEqual(l.average(), s / 20);
    }

    [TestMethod]
    public void TestCountValue()
    {
        MyList l1 = new MyList();
        for (int i = 0; i < 10; ++i)
        {
            l1.add(i);
            l1.add(i * i);
        }
        Assert.AreEqual(l1.count(-1), 0);
        Assert.AreEqual(l1.count(0), 2);
        Assert.AreEqual(l1.count(1), 2);
        Assert.AreEqual(l1.count(2), 1);
        Assert.AreEqual(l1.count(3), 1);
        Assert.AreEqual(l1.count(4), 2);
        Assert.AreEqual(l1.count(5), 1);
        Assert.AreEqual(l1.count(6), 1);
        Assert.AreEqual(l1.count(7), 1);
        Assert.AreEqual(l1.count(8), 1);
        Assert.AreEqual(l1.count(9), 2);
        Assert.AreEqual(l1.count(10), 0);
        Assert.AreEqual(l1.count(16), 1);
    }

    [TestMethod]
    public void TestRemoveFirst()
    {
        MyList l1 = new MyList();
        for (int i = 0; i < 10; ++i)
        {
            l1.add(i);
            l1.add(i * i);
        }
        Assert.AreEqual(l1.count(81), 1);
        l1.removeFirst();
        Assert.AreEqual(l1.count(), 19);
        Assert.AreEqual(l1.count(81), 0);
        Assert.AreEqual(l1.count(-1), 0);
        Assert.AreEqual(l1.count(0), 2);
        Assert.AreEqual(l1.count(1), 2);
        Assert.AreEqual(l1.count(2), 1);
        Assert.AreEqual(l1.count(3), 1);
        Assert.AreEqual(l1.count(4), 2);
        Assert.AreEqual(l1.count(5), 1);
        Assert.AreEqual(l1.count(6), 1);
        Assert.AreEqual(l1.count(7), 1);
        Assert.AreEqual(l1.count(8), 1);
        Assert.AreEqual(l1.count(9), 2);
        Assert.AreEqual(l1.count(10), 0);
        Assert.AreEqual(l1.count(16), 1);
    }

    [TestMethod]
    public void TestInsert()
    {
        MyList l1 = new MyList();
        for (int i = 9; i >= 0; --i)
        {
            l1.add(i);
        }
        for (int i = 0; i <= 10; ++i)
        {
            l1.add(i, 2 * i);
        }
        for (int i = 0; i < 10; ++i)
        {
            Assert.AreEqual(l1.get(2 * i), i, "i=" + i);
            Assert.AreEqual(l1.get(2 * i + 1), i);
        }
        Assert.AreEqual(l1.get(20), 10);
    }
}

这就是我的能力：

public class MyList
{
    class Element
    {
        public float value;
        public Element next;
    }

    Element first;

    public MyList()
    {
        first = null;
    }

    public void add(float x)
    {
        Element e = new Element();
        e.value = x;
        e.next = first;
        first = e;
    }
    public float get(int i)
    {
        if (first == null)
        {
            throw new Exception("Empty list... no elements inside");
        }

        Element tmp = first;
        for (int j = 0; j < i; ++j)
        {
            tmp = tmp.next;
            if (tmp == null)
            {
                throw new Exception("...");
            }
        }

        return tmp.value;
    }

    public void print()
    {
        Element e = first;
        while (e != null)
        {
            Console.WriteLine(e.value);
            e = e.next;
        }
    }

    public bool find(float x)
    {
        Element e = first;
        while (e != null)
        {
            if (e.value == x)
            {
                return true;
            }
            e = e.next;
        }

        return false;
    }

    public float max()
    {
        float G = 0;
        for (Element e = first; e != null; e = e.next)
        {
            if (e.value > G)
            {
                G = e.value;
            }
        }

        return G;
    }

    public int count()
    {
        Element e = first;
        int c = 0;
        while (e != null)
        {
            c++;
            e = e.next;
        }

        return c;
    }

    public int count(float x)
    {
        int c = 0;
        for (Element e = first; e != null; e = e.next)
        {
            if (e.value == x)
            {
                c++;
            }
        }

        return c;
    }

    public float sum()
    {
        float S = 0;
        for (Element e = first; e != null; e = e.next)
        {
            S += e.value;
        }

        return S;
    }

    public float average()
    {
        return sum() / count();
    }

    public void removeFirst()
    {
        Element e = first;
        first = e.next;
    }

    public void add(float x, int pos)
    {
        //I have absolutely no idea how to implement this fonction.
    }
}

Answer 1

它类似于get（）方法中的代码。

将问题分解为更小的问题

pos = 0吗？
- 如果是，请创建一个新根并将其指向旧根
- 如果没有，循环（pos）次并创建一个新元素。然后将新元素的下一个属性设置为当前元素的下一个属性。将当前元素next属性设置为新元素

public void add(float x, int pos)
{
    if(pos == 0)
    {
        // create a new root and point the new root to the existing root
    }
    else
    {
        Element tmp = first;
        for(int i = 0; i < pos; i++)
        {
            tmp = tmp.next;
        }

        // create new element
        // set new element next property to tmp.next
        // set tmp.next to new element
    }
}

C＃链接列表（将元素添加到定义的位置）

1 个答案: