Introduction and usage of hashtable in C #

I. Introduction

Terms: A hash table is a data structure that is directly accessed based on the key value. That is to say, It maps the key value to a location in the table to access records to speed up the search. This ing function is called a hash function, and the array storing records is called a hash function.

Advantages of hashtable tables: Hashtable is a container provided by the system. Collections namespace. The key/value in hashtable is of the object type, so hashtable can support any type of key/value Key/value pairs.

The advantage of hashtable lies in its indexing method and speed.Very fast.

Ii. Simple operations on Hash Tables

Add a keyValue key-value pair in the hash table: hashtableobject. Add (Key, value );

Remove a keyValue key-value pair in the hash table: hashtableobject. Remove (key );

Remove all elements from the hash table: hashtableobject. Clear ();

Determine whether the hash table contains the specified key: hashtableobject. Contains (key );

The following ConsoleProgramAll of the above operations will be included:

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Using System ; Using System. Collections ; // This namespace must be introduced when file uses hashtable. Class Hashtable { Public Static Void Main( ) { Hashtable HT = New Hashtable ( ) ; // File to create a hashtable instance Ht. Add ( E, E ) ; // Add a keyValue pair Ht. Add ( A, ) ; Ht. Add ( C, C ) ; Ht. Add ( B, B ) ; String S = ( String ) HT [ A ] ; If ( Ht. Contains ( E ) ) // File: determines whether a hash table contains a specific key. The return value is true or false. Console. Writeline ( The E keyexist ) ; Ht. Remove ( C ) ; // Remove a keyValue pair Console. Writeline ( HT [ A ] ) ; // Output Ht. Clear ( ) ; // Remove all elements Console. Writeline ( HT [ A ] ) ; // File. No output is provided here. } }

3. traverse the hash table

Dictionaryentry object is required to traverse a hash table,CodeAs follows:

 For  ( Dictionaryentry de In HT )  // Fileht is a hashtable instance.  { Console. Writeline  ( De. Key  )  ;  // De. Key corresponds to the key-value pair of keyValue Console. Writeline  ( De. Value  )  ;  // De. Key corresponds to the keyValue key-Value Pair Value  } 

4. Sorting hash tables

The definition of sorting hash tables here is to re-arrange the keys in the key-Value Pair according to certain rules, but in fact this definition cannot be implemented, because we cannot re-arrange keys directly in hashtable, if hashtable needs to provide output of certain rules, we can adopt a work und:

Arraylist akeys =  New Arraylist ( Ht. Keys  )  ;  // File do not forget to import system. Collections Akeys. Sort  (  )  ;  // Sort files alphabetically.  For  (  String Skey In Akeys )  { Console. Write  ( Skey +   )  ; Console. Writeline  ( HT[ Skey ]  )  ;  // Output after sorting  } 

ArticleFrom:Xiaofeng caotangHttp://www.cnitman.com/csharp-hashtable-usage-introduce/