[C/C ++ standard library] _ [elementary] _ [map lookup Function Analysis]

[C/C ++ standard library] _ [elementary] _ [map lookup Function Analysis]

Scenario:

1. map is efficient in searching for objects with non-numeric indexes (which can be a vector for non-repeated numeric indexes), because the implementation of the Red/black tree makes logarithmic time efficient in searching and inserting.

2. map is a very practical data structure.

3. You can use multimap to store duplicate keys. The scenario is one-to-many. For example, a contact corresponds to multiple groups.

 

 

Void TestMap () {// map is generally implemented through the red/black tree. logarithmic timetypedef map
 
  
TMap; typedef multimap
  
   
TTMap; TMap m; m [1] = 8; m [2] = 10; m [5] = 11; TTMap mm; mm. insert (pair
   
    
(); Mm. insert (pair
    
     
(2, 10); mm. insert (pair
     
      
(1, 11); mm. insert (pair
      
        (1, 12); // countint count = 0; if (count = m. count (1) {// 1. if you want to use it, you still need to use [] to find it once. // output: m. count (1): 1 cout <"m. count (1): "<count <endl;} if (count = mm. count (1) {// 1. if you want to use it, you still need to use interval _range to find it once. // multimap does not have the [] OPERATOR overload, because the key is not unique. // output mm. count (1): 3 cout <"mm. count (1): "<count <endl;} // view the implementation of count, which is implemented using interval _range. // performance_range is a continuous iterator composed of all values equal to the key. // the first pair is the first iterator that matches the key, and the second is the first iterator that is greater than the key. // mappair
       
         Values = m. struct _range (1); TMap: iterator B = values. first; // output map struct _range: 8 while (B! = Values. second) {cout <"map into _range:" <(* B). second <endl; ++ B;} // multimappair
        
          Valuess = mm. required _range (1); TTMap: iterator bs = valuess. first; // output: // multimap upload _range: 8 // multimap upload _range: 11 // multimap upload _range: 12 while (bs! = Valuess. second) {cout <"multimap upload _range:" <(* bs ). second <endl; ++ bs;} // Find. Find the first iterator that matches the key. The second iterator cannot be found. If you need to Find the second iterator, use performance_range // Find to use lower_bound for search. lower_bound is used to Find the first element greater than or equal to the key. // similar to upper_bound to find the first element greater than the key. TMap: iterator ite = m. find (1); if (ite! = M. end () {// 1. use iterator directly. // output: m. find 8 cout <"m. find "<(* ite ). second <endl;} ite = m. lower_bound (3); if (ite! = M. end () {// output m. lower_bound key 5 m. lower_bound 11 cout <"m. lower_bound key "<(* ite ). first <"m. lower_bound "<(* ite ). second <endl;} // multimapbs = mm. lower_bound (1); if (ite! = M. end () {// output: mm. lower_bound key 1mm. lower_bound 8 cout <"mm. lower_bound key "<(* bs ). first <"mm. lower_bound "<(* bs ). second <endl;} bs = mm. upper_bound (1); if (ite! = M. end () {// output: mm. upper_bound key 2mm. upper_bound 10 cout <"mm. upper_bound key "<(* bs ). first <"mm. upper_bound "<(* bs ). second <endl ;}} int _ tmain (int argc, _ TCHAR * argv []) {TestMap (); return 0 ;}
        
       
      
     
    
   
  
 

 

Source code of the Standard Library:

 

size_type count(const key_type& _Keyval) const{// count all elements that match _Keyval_Paircc _Ans = equal_range(_Keyval);size_type _Num = 0;_Distance(_Ans.first, _Ans.second, _Num);return (_Num);}iterator find(const key_type& _Keyval){// find an element in mutable sequence that matches _Keyvaliterator _Where = lower_bound(_Keyval);return (_Where == end()|| _DEBUG_LT_PRED(this->comp,_Keyval, this->_Key(_Where._Mynode()))? end() : _Where);}