C# 在stringbuider-C中查看项目的时间复杂性#

我在

StringBuilder

中保存了一些长文本，我想获取一些特定的项目

StringBuilder builder = new StringBuilder();
//fill builder
int i = someNumber();
char ch = builder[i];

最后一条指令（

char ch=builder[i]

）的时间复杂度是多少？它是常数吗

O（1）

还是线性的

O（i）

---

它是一个常数，因为你给出了元素的精确位置，所以在这个例子中是O（1）。这里有更多细节

---

这是一个常数，因为您给出了获取元素的确切位置。因此在本例中为O（1）。这里有更多细节

---

charch=builder[i]

是O（1）

---

因为StringBuilder使用了数组索引。

char ch=builder[i]

是O（1）

因为StringBuilder使用数组索引。

根据

StringBuilder

类将字符串存储在字符数组中

通过属性getter

this[int index]

访问此数组会进行一些检查，然后返回数组项：

    internal char[] m_ChunkChars;                // The characters in this block
    //...more stuff

    [System.Runtime.CompilerServices.IndexerName("Chars")]
    public char this[int index] {
        // 

        get {
            StringBuilder chunk = this;
            for (; ; )
            {
                int indexInBlock = index - chunk.m_ChunkOffset;
                if (indexInBlock >= 0)
                {
                    if (indexInBlock >= chunk.m_ChunkLength)
                        throw new IndexOutOfRangeException();
                    return chunk.m_ChunkChars[indexInBlock];
                }
                chunk = chunk.m_ChunkPrevious;
                if (chunk == null)
                    throw new IndexOutOfRangeException();
            }
        }
        //... more stuff
    }

因此，复杂性是O（1）或恒定的访问时间。

根据

StringBuilder

类将字符串存储在字符数组中

通过属性getter

this[int index]

访问此数组会进行一些检查，然后返回数组项：

    internal char[] m_ChunkChars;                // The characters in this block
    //...more stuff

    [System.Runtime.CompilerServices.IndexerName("Chars")]
    public char this[int index] {
        // 

        get {
            StringBuilder chunk = this;
            for (; ; )
            {
                int indexInBlock = index - chunk.m_ChunkOffset;
                if (indexInBlock >= 0)
                {
                    if (indexInBlock >= chunk.m_ChunkLength)
                        throw new IndexOutOfRangeException();
                    return chunk.m_ChunkChars[indexInBlock];
                }
                chunk = chunk.m_ChunkPrevious;
                if (chunk == null)
                    throw new IndexOutOfRangeException();
            }
        }
        //... more stuff
    }

---

因此，复杂性是O（1）或恒定访问时间。

查看

StringBuilder

的实现，它是O（1），因为它是使用

char[]

    //
    //
    //  CLASS VARIABLES
    //
    //
    internal char[] m_ChunkChars;                // The characters in this block
    internal StringBuilder m_ChunkPrevious;      // Link to the block logically before this block
    internal int m_ChunkLength;                  // The index in m_ChunkChars that represent the end of the block
    internal int m_ChunkOffset;                  // The logial offset (sum of all characters in previous blocks)
    internal int m_MaxCapacity = 0;

---

查看

StringBuilder

的实现，它是O（1），因为它使用

char[]

    //
    //
    //  CLASS VARIABLES
    //
    //
    internal char[] m_ChunkChars;                // The characters in this block
    internal StringBuilder m_ChunkPrevious;      // Link to the block logically before this block
    internal int m_ChunkLength;                  // The index in m_ChunkChars that represent the end of the block
    internal int m_ChunkOffset;                  // The logial offset (sum of all characters in previous blocks)
    internal int m_MaxCapacity = 0;