雙向鏈表宛如一列火車,剛發明的時候只有一個頭,若是它的行駛路線爲:A->B->C->D->E->F->G->H->I->J->K->A
這個時候有一批貨物須要從K運到J,那麼它的運輸路線必定是:
K->A->B->C->D->E->F->G->H->I->J
因此後來火車就有了兩個頭,因而可知雙向鏈表的重要性!!!node
雙向鏈表:在單鏈表結點上增添了一個指針域,指向當前結點的前驅。這樣就能夠方便的由其後繼來找到其前驅,而實現輸出終端結點到開始結點的數據序列。
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雙向鏈表的結點結構svg
/// <summary>
/// 雙向鏈表節點
/// </summary>
/// <typeparam name="T"></typeparam>
public class BdNode<T>
{
public T data { set; get; }
public BdNode<T> next { set; get; }
public BdNode<T> prev { set; get; }
public BdNode(T val, BdNode<T> prev, BdNode<T> next)
{
this.Data = val;
this.Prev = prev;
this.Next = next;
}
public BdNode(T data, BdNode<T> next)
{
this.data = data;
this.next = next;
this.prev = null;
}
public BdNode(BdNode<T> next)
{
this.data = default(T);
this.next = next;
this.prev = null;
}
public BdNode(T data)
{
this.data = data;
this.next = null;
this.prev = null;
}
public BdNode()
{
data = default(T);
next = null;
prev = null;
}
public T Data
{
set { this.data = value; }
get { return this.data; }
}
public BdNode<T> Prev
{
get { return prev; }
set { prev = value; }
}
public BdNode<T> Next
{
get { return next; }
set { next = value; }
}
}
雙向鏈表還能做爲雙向循環鏈表使用,下圖爲雙向循環鏈表的結構圖:
this
雙向鏈表的插入:
總共四個步驟:
步驟1:a.next=a2;
步驟2:a.prev=a1;
步驟3:a1.next=a;
步驟4:a2.prev=a;
插入順序按圖標所示,操做雖然簡單可是不能寫反,順序很重要!
其實現代碼以下:spa
/// <summary>
/// 在最後附加元素
/// </summary>
/// <param name="item"></param>
public void Append(T item)
{
BdNode<T> d = new BdNode<T>(item);
BdNode<T> n = new BdNode<T>();
if (Head == null)
{
Head = d;
return;
}
n = Head;
while (n.Next != null)
{
n = n.Next;
}
n.Next = d;
d.Prev = n;
}
//前插
public void InsertBefore(T item, int i)
{
if (IsEmpty() || i < 0)
{
Console.WriteLine("List is empty or Position is error!");
return;
}
//在最開頭插入
if (i == 0)
{
BdNode<T> q = new BdNode<T>(item);
q.Next = head;//把"頭"改爲第二個元素
head.Prev = q;
head = q;//把本身設置爲"頭"
return;
}
BdNode<T> n = head;
BdNode<T> d = new BdNode<T>();
int j = 0;
//找到位置i的前一個元素d
while (n.Next != null && j < i)
{
d = n;
n = n.Next;
j++;
}
if (n.Next == null) //說明是在最後節點插入(即追加)
{
BdNode<T> q = new BdNode<T>(item);
n.Next = q;
q.Prev = n;
q.Next = null;
}
else
{
if (j == i)
{
BdNode<T> q = new BdNode<T>(item);
d.Next = q;
q.Prev = d;
q.Next = n;
n.Prev = q;
}
}
}
/// <summary>
/// 在位置i後插入元素item
/// </summary>
/// <param name="item"></param>
/// <param name="i"></param>
public void InsertAfter(T item, int i)
{
if (IsEmpty() || i < 0)
{
Console.WriteLine("List is empty or Position is error!");
return;
}
if (i == 0)
{
BdNode<T> q = new BdNode<T>(item);
q.Next = head.Next;
head.Next.Prev = q;
head.Next = q;
q.Prev = head;
return;
}
BdNode<T> p = head;
int j = 0;
while (p != null && j < i)
{
p = p.Next;
j++;
}
if (j == i)
{
BdNode<T> q = new BdNode<T>(item);
q.Next = p.Next;
if (p.Next != null)
{
p.Next.Prev = q;
}
p.Next = q;
q.Prev = p;
}
else
{
Console.WriteLine("Position is error!");
}
}
刪除操做:只需把被刪除節點的前一個節點的next指針指向它下一個節點的下一個節點,再把被刪除節點的下一個節點的prev指針指向它前一個節點的前一個節點就OK了,以下圖所示:
其實現代碼以下:指針
/// <summary>
/// 刪除位置i的元素
/// </summary>
/// <param name="i"></param>
/// <returns></returns>
public T RemoveAt(int i)
{
if (IsEmpty() || i < 0)
{
Console.WriteLine("Link is empty or Position is error!");
return default(T);
}
BdNode<T> q = new BdNode<T>();
if (i == 0)
{
q = head;
head = head.Next;
head.Prev = null;
return q.Data;
}
BdNode<T> p = head;
int j = 0;
while (p.Next != null && j < i)
{
j++;
q = p;
p = p.Next;
}
if (j == i)
{
p.Next.Prev = q;
q.Next = p.Next;
return p.Data;
}
else
{
Console.WriteLine("The node is not exist!");
return default(T);
}
}
雙向鏈表的好處在於:
一、對鏈表數據的遍歷操做不單單能向後遍歷(如單鏈表),並且還可以向前遍歷尋找元素,對鏈表數據的操做更加靈活。
二、能夠直接刪除某一個數據元素,我的認爲這是比較重要的一方面,由於對單鏈表而言,若是要刪除某一個數據元素,須要遍歷至此元素以前的一個結點才能刪除,而雙向鏈表能夠遍歷到某一元素,而後能夠直接對它進行刪除操做。code