數據結構與算法-單向鏈表

 

概述

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因爲最近在工做中須要用到樹形結構來解決一些問題，因此萌生了系統學習「數據結構和算法」的想法，因而乎從最簡單的表結構開始。因爲數組是最簡單的表結構的實現，也是各個編程語言內置的數據類型，因此不作更多的記錄。表結構中如下實現打算學習：

• LinkedList
• Stack
• Queue
• HashTable
• Dictionary

本篇爲學習數據結構的第一篇隨筆，從最簡單的單向鏈表開始吧。

 

實現（C#）

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平臺：dotNet Core 1.0， C#

IDE：VSCode

若是考慮算法複用的話，能夠實現泛型。

 1 public class SingleLinkedList  2  {  3         //Inner class, represents a node of linked list. Each node consists of data and a link to next node
 4         class Node  5  {  6             public Node() { }  7             public Node(object item)  8  {  9                 Data = item;  10                 Next = null;  11  }  12             public object Data { get; set; }  13             public Node Next { get; set; }  14 
 15             public override string ToString()  16  {  17                 return "Node:" + Data.ToString();  18  }  19  }  20 
 21         public SingleLinkedList()  22  {  23             header = null;  24  }  25 
 26         #region Public API
 27 
 28         //Add item before first node
 29         public void AddFirst(object item)  30  {  31             if (header == null)  32  {  33                 header = new Node(item);  34  }  35             else
 36  {  37                 var newNode = new Node(item);  38                 newNode.Next = header;  39                 header = newNode;  40  }  41  }  42 
 43         //Add item after last node
 44         public void AddLast(object item)  45  {  46             if (header == null)  47  {  48                 header = new Node(item);  49  }  50             else
 51  {  52                 LastNode().Next = new Node(item);  53  }  54  }  55 
 56         public void Insert(int index, object item)  57  {  58             if (index < 0) throw new ArgumentOutOfRangeException();  59             if (index == 0)  60  {  61  AddFirst(item);  62                 return;  63  }  64             if (header == null) throw new ArgumentOutOfRangeException();  65 
 66             var node = GetNode(index - 1);  67             var newNode = new Node(item);  68             newNode.Next = node.Next;  69             node.Next = newNode;  70  }  71 
 72         public object Get(int index)  73  {  74             return GetNode(index).Data;  75  }  76 
 77         //Find index of specified data
 78         public int IndexOf(object item)  79  {  80             if (header == null) return -1;  81 
 82             var curIndex = 0;  83             for (var cur = new Node { Next = header }; cur.Next != null; cur = cur.Next, curIndex++)  84  {  85                 if (!cur.Next.Data.Equals(item)) continue;  86                 return curIndex;  87  }  88 
 89             return -1;  90  }  91 
 92         //Remove specified data of its first occurance
 93         public void Remove(object item)  94  {  95             if (header == null) return;  96 
 97             //Add a fake node pointing to header, so we don't need set up a local variable pointing to header. This is simple. Nice trick.
 98             for (var cur = new Node { Next = header }; cur.Next != null; cur = cur.Next)  99  { 100                 if (!cur.Next.Data.Equals(item)) continue; 101                 if (cur.Next == header) 102  { 103                     header = header.Next; 104  } 105                 else
106  { 107                     cur.Next = cur.Next.Next; 108  } 109  } 110  } 111 
112         //此方法能夠理解爲先獲取index-1位置的Node，而後設置此Node的下一個節點跳過index處的節點
113         public void RemoveAt(int index) 114  { 115             if (index < 0 || header == null) throw new ArgumentOutOfRangeException(); 116             else if (index == 0) 117  { 118                 header = header.Next; 119  } 120             else
121  { 122                 Node pre = GetNode(index - 1); 123                 pre.Next = pre.Next.Next; 124  } 125  } 126 
127         public bool Contains(object item) 128  { 129             if (header == null) return false; 130             var current = header; 131             while (current != null && !current.Data.Equals(item)) 132  { 133                 current = current.Next; 134  } 135             return current != null; 136  } 137 
138         public void Clear() 139  { 140             header = null; 141  } 142 
143         public bool IsEmpty() 144  { 145             return header == null; 146  } 147 
148         public int Count() 149  { 150             if (IsEmpty()) return 0; 151             int count = 1; 152             for (var cur = header; cur.Next != null; cur = cur.Next, count++) 153  { 154  } 155             return count; 156  } 157 
158         public override string ToString() 159  { 160             if (header == null) return "Empty"; 161             StringBuilder sb = new StringBuilder(); 162             for (Node current = header; current != null; current = current.Next) 163  { 164  sb.Append(current.Data.ToString()); 165                 if (current.Next != null) sb.Append("->"); 166  } 167             return sb.ToString(); 168  } 169 
170         #endregion
171 
172         #region Private Method
173 
174         private Node LastNode() 175  { 176             if (header == null) throw new InvalidOperationException(); 177 
178             var current = header; 179             while (current.Next != null) 180  { 181                 current = current.Next; 182  } 183             return current; 184  } 185 
186         private Node GetNode(int index) 187  { 188             if (header == null) throw new ArgumentOutOfRangeException(); 189 
190             int curIndex = 0; 191             var cur = header; 192             while (cur != null && curIndex != index) 193  { 194                 cur = cur.Next; 195                 curIndex++; 196  } 197 
198             if (cur == null) 199  { 200                 throw new ArgumentOutOfRangeException(); 201  } 202             else
203  { 204                 return cur; 205  } 206  } 207 
208 
209         #endregion
210 
211         #region Fields
212 
213         private Node header; 214 
215         #endregion
216     }

 

測試代碼

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 1 public static void Main(string[] args)
 2         {
 3             Can_Add_First();
 4             Can_Add_Last();
 5             Can_Insert();
 6             Other();
 7 
 8             Console.ReadKey();
 9         }
10 
11         static void Can_Add_First()
12         {
13             var list = new SingleLinkedList();
14             //add when list is empty
15             list.AddFirst("First");
16             Expect(list, "First");
17             //add when list is not empty
18             list.AddFirst("Second");
19             list.AddFirst("Third");
20             Expect(list, "Third->Second->First");
21         }
22 
23         static void Can_Add_Last()
24         {
25             var list = new SingleLinkedList();
26             //add when list is empty
27             list.AddLast("First");
28             Expect(list, "First");
29             //add when list is not empty
30             list.AddLast("Second");
31             list.AddLast("Third");
32             Expect(list, "First->Second->Third");
33         }
34 
35         static void Can_Insert()
36         {
37             var list = new SingleLinkedList();
38             //insert when list is empty
39             list.Insert(0, "First");
40             Expect(list, "First");
41             //insert when list is not empty
42             list.Insert(1, "Second");
43             Expect(list, "First->Second");
44             list.Insert(1, "Third");
45             Expect(list, "First->Third->Second");
46             list.Insert(0, "Forth");
47             Expect(list, "Forth->First->Third->Second");
48         }
49 
50         static void Other()
51         {
52             var list = new SingleLinkedList();
53             list.AddLast("First");
54             list.AddLast("Second");
55             list.AddLast("Third");
56             Console.WriteLine("object Get(int) Passed: " + (list.Get(1) as string == "Second"));
57             
58             Console.WriteLine("int IndexOf(object) Passsed: " + ((int)list.IndexOf("Third") == 2));
59             Console.WriteLine("int IndexOf(object) Passsed: " + ((int)list.IndexOf("Forth") == -1));
60             
61             list.Remove("First");
62             Expect(list, "Second->Third");
63             list.RemoveAt(1);
64             Expect(list, "Second");
65             
66             Console.WriteLine("bool Contains(object) Passed: " + (list.Contains("Second") == true));
67             Console.WriteLine("bool Contains(object) Passed: " + (list.Contains("First") == false));
68             Console.WriteLine("int Count() Passed: " + (list.Count() == 1));
69             Console.WriteLine("bool IsEmpty() Passed: " + (list.IsEmpty() == false));
70             
71             list.Clear();
72             Console.WriteLine("int Count() Passed: " + (list.Count() == 0));
73             Console.WriteLine("bool IsEmpty() Passed: " + (list.IsEmpty() == true));
74         }