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Data dictionary in C ＃

2022-07-06 10:58:00 【Dotnet cross platform】

Preface

Surfing the Internet as usual this morning , I saw an interview question chatting in the wechat group of maijiage , It's interesting , Here is a brief share of the conclusions Dictionary Dictionaries .

Yes 50w individual int Type of number , Now we need to judge whether there are duplicate numbers , Please briefly explain .

If this topic let me do , The first feeling may be directed to two for loop , Simply make a judgment and solve . But I saw the discussion of several big guys , I found that my knowledge is shallow .

Is this question about the application of business code cycle ？ Definitely not .

We know , In verifying a piece of code or a program algorithm, the perfect indicators are space complexity and time complexity . Judge by these two indicators .

Spatial complexity ：

It refers to the execution of an algorithm program , How much storage capacity is temporarily occupied per unit time . use S(n)=O(f(n)) To express .

Time complexity ：

It refers to the execution of an algorithm program , How much time will it take .

In general , The number of times the basic operations are repeated in the algorithm is the scale of the problem n A function of , use T(n) Express , If there is an auxiliary function f(n), Properly n Approaching infinity ,T(n)/f(n) The limit value of is a constant not equal to zero , said f(n) yes T(n) Functions of the same order of magnitude of , Write it down as T(n)=O(f(n)), be called O(f(n)) Time complexity of the algorithm .

For example, the time complexity of insertion sorting is O(n^2), The space complexity is O(1).

The advantages and disadvantages of an algorithm are mainly measured from two aspects: the execution time of the algorithm and the required storage space .

During the discussion in the Group , There is an array array, Key value pair , And data dictionary Dictionary( A key value pair ). Finally, I feel like using Dictionary Store this 50w individual int Data of type , Use it key perhaps value To determine if there are duplicate values .

Now that I see this , Today we will simply review Dictionary, See what charm it has .

Dictionary<TKey,TValue> Dictionaries

according to MSDN Records on , Say it is a set of keys and values . Provide a set of keys to a set of values mapping . Each addition to the dictionary contains a value and its associated key . The speed of retrieving values using its keys very fast , near O(1).

Dictionary<TKey,TValue> This class is implemented as a hash table , The speed of retrieval depends on the quality of the hash algorithm for the specified type TKey.

Other features are briefly summarized as follows

Must contain a namespace System.Collection.Generic
Dictionary Every element in it is a key value pair
The key must be unique , The value does not need to be unique
Keys and values can be of any type
The time complexity of reading a value through a key is close to O(1), Search speed is very fast , than list Wait a lot faster
The partial order between key value pairs can not be defined
You can search by key value 、 Insert 、 Delete a key value pair , It is very troublesome to implement these with arrays

Here is about Dictionary Some of CRUD operation .

Definition dictionary 、 Add key value 、 Value 、 Change value 、 Traverse key、 Traverse value、 Remove elements 、 Empty all elements

// Definition 
  static Dictionary<int, string> ahuiInfo = new Dictionary<int, string>();
  static void Main(string[] args)
  {
      // Add key value 
      ahuiInfo.Add(1," A Hui ");
      ahuiInfo.Add(2, " Arabinase ");
      ahuiInfo[2] = " Al I "
      // Value 
      var name=ahuiInfo[0].ToString();
      Console.WriteLine(""+name
      // Modified value 
      ahuiInfo[0] = " aunt ";
      Console.WriteLine("" + ahuiInfo[0].ToString()
      // Traverse key and value
      foreach (var key in ahuiInfo.Keys)
      {
          Console.WriteLine(""+key.ToString());
    
      foreach (var value in ahuiInfo.Values)
      {
          Console.WriteLine(" "+value.ToString());
    
      // Ergodic dictionary 
      foreach(KeyValuePair<int ,string> kvp in ahuiInfo)
      {
          Console.WriteLine("key="+kvp.Key+",value="+kvp.Value);
    
      // Remove elements 
      ahuiInfo.Remove(0
      // Judge whether the key exists 
      if (ahuiInfo.ContainsKey(0))
      {
          Console.WriteLine("true");
      }
      else
      {
          Console.WriteLine("false");
      }
  }
}