c++ - Counting number of occurrences in a range within an unordered_map -

i have unordered_map set as:

unordered_map<int, deque<my_struct>> table; 

when read values program, do:

 table[int].push_back(obj); 

what want able if i'm given 2 integer variables, want able find number of keys occur between two.

so if in table have code like

  table[49].push_back(obj);   table[59].push_back(obj);   table[60].push_back(obj); 

if execute search function(which i'm trying write) between key values of 45 , 65, should have 3 results.

i'm not sure how go in efficient manner. ideas helpful. you.

if using std::unordered_map don't think have choice loop on integers 45 65 , use find check if key exists in unordered_map:

using my_table = std::unordered_map<int, std::deque<my_struct>>;  int count(const my_table& table, int begin, int end) {   int sum = 0;   (int = begin; != end; ++i) {     auto find_result = table.find(i);     if (find_result != table.end())         sum++;   }   return sum; } 

but may not efficient. if use std::map instead elements ordered can achieved more efficiently:

using my_table = std::map<int, std::deque<my_struct>>;  int count(const my_table& table, int begin, int end) {   auto begin_itr = table.lower_bound(begin);   if (begin_itr == table.end())       return 0;   auto end_itr = table.lower_bound(end);   return std::distance(begin_itr, end_itr); } 

i've used std::map::lower_bound function.

depending on how sparse map might consider using std::vector<std::deque<my_struct>> flat map.

live demo.