How to determine whether a value exists in map in C++
I understand that std::map is (Key, Value) pairs.
I want to search through the values of a map. Let us say that I want to find the highest value among the values in the std::map. How can I do that ?
For example let me consider a map like this:
John -> 100
Jeffrey -> 200
Krishna -> 147
I think it will be similar to this , but I am not sure.
for (auto it=m.begin(); it!=m.end(); it++)
{
if (it->second == 500)
{
cout << "Found";
}
else {
continue;}
}
Instead of iterating through std::map, is there any other inbuilt method using which I can check if a value exists in a std::map with O(1) time complexity ?
c++ stl hashtable
asked Nov 23 '18 at 17:06
NitzNitz
64
|
show 1 more comment
I understand that std::map is (Key, Value) pairs.
I want to search through the values of a map. Let us say that I want to find the highest value among the values in the std::map. How can I do that ?
For example let me consider a map like this:
John -> 100
Jeffrey -> 200
Krishna -> 147
I think it will be similar to this , but I am not sure.
for (auto it=m.begin(); it!=m.end(); it++)
{
if (it->second == 500)
{
cout << "Found";
}
else {
continue;}
}
Instead of iterating through std::map, is there any other inbuilt method using which I can check if a value exists in a std::map with O(1) time complexity ?
c++ stl hashtable
asked Nov 23 '18 at 17:06
NitzNitz
64
well, yes :) that's it
– OznOg
Nov 23 '18 at 17:07
2
en.cppreference.com/w/cpp/container/map
– Lightness Races in Orbit
Nov 23 '18 at 17:08
are you actually searching for the max or a random value?
– OznOg
Nov 23 '18 at 17:08
1
en.cppreference.com/w/cpp/algorithm
– Lightness Races in Orbit
Nov 23 '18 at 17:09
1
First you say map then you say hashmap - they are different make your mind
– Slava
Nov 23 '18 at 17:09
|
show 1 more comment
I understand that std::map is (Key, Value) pairs.
I want to search through the values of a map. Let us say that I want to find the highest value among the values in the std::map. How can I do that ?
For example let me consider a map like this:
John -> 100
Jeffrey -> 200
Krishna -> 147
I think it will be similar to this , but I am not sure.
for (auto it=m.begin(); it!=m.end(); it++)
{
if (it->second == 500)
{
cout << "Found";
}
else {
continue;}
}
Instead of iterating through std::map, is there any other inbuilt method using which I can check if a value exists in a std::map with O(1) time complexity ?
c++ stl hashtable
asked Nov 23 '18 at 17:06
NitzNitz
64
I understand that std::map is (Key, Value) pairs.
I want to search through the values of a map. Let us say that I want to find the highest value among the values in the std::map. How can I do that ?
For example let me consider a map like this:
John -> 100
Jeffrey -> 200
Krishna -> 147
I think it will be similar to this , but I am not sure.
for (auto it=m.begin(); it!=m.end(); it++)
{
if (it->second == 500)
{
cout << "Found";
}
else {
continue;}
}
Instead of iterating through std::map, is there any other inbuilt method using which I can check if a value exists in a std::map with O(1) time complexity ?
c++ stl hashtable
c++ stl hashtable
asked Nov 23 '18 at 17:06
NitzNitz
64
asked Nov 23 '18 at 17:06
NitzNitz
64
edited Jan 29 at 14:02
Nitz
asked Nov 23 '18 at 17:06
NitzNitz
64
asked Nov 23 '18 at 17:06
NitzNitz
64
asked Nov 23 '18 at 17:06
NitzNitz
64
64
well, yes :) that's it
– OznOg
Nov 23 '18 at 17:07
2
en.cppreference.com/w/cpp/container/map
– Lightness Races in Orbit
Nov 23 '18 at 17:08
are you actually searching for the max or a random value?
– OznOg
Nov 23 '18 at 17:08
1
en.cppreference.com/w/cpp/algorithm
– Lightness Races in Orbit
Nov 23 '18 at 17:09
1
First you say map then you say hashmap - they are different make your mind
– Slava
Nov 23 '18 at 17:09
|
show 1 more comment
well, yes :) that's it
– OznOg
Nov 23 '18 at 17:07
2
en.cppreference.com/w/cpp/container/map
– Lightness Races in Orbit
Nov 23 '18 at 17:08
are you actually searching for the max or a random value?
– OznOg
Nov 23 '18 at 17:08
1
en.cppreference.com/w/cpp/algorithm
– Lightness Races in Orbit
Nov 23 '18 at 17:09
1
First you say map then you say hashmap - they are different make your mind
– Slava
Nov 23 '18 at 17:09
well, yes :) that's it
– OznOg
Nov 23 '18 at 17:07
well, yes :) that's it
– OznOg
Nov 23 '18 at 17:07
2
2
en.cppreference.com/w/cpp/container/map
– Lightness Races in Orbit
Nov 23 '18 at 17:08
en.cppreference.com/w/cpp/container/map
– Lightness Races in Orbit
Nov 23 '18 at 17:08
are you actually searching for the max or a random value?
– OznOg
Nov 23 '18 at 17:08
are you actually searching for the max or a random value?
– OznOg
Nov 23 '18 at 17:08
1
1
en.cppreference.com/w/cpp/algorithm
– Lightness Races in Orbit
Nov 23 '18 at 17:09
en.cppreference.com/w/cpp/algorithm
– Lightness Races in Orbit
Nov 23 '18 at 17:09
1
1
First you say map then you say hashmap - they are different make your mind
– Slava
Nov 23 '18 at 17:09
First you say map then you say hashmap - they are different make your mind
– Slava
Nov 23 '18 at 17:09
|
show 1 more comment
2 Answers
2
active
oldest
votes
Q1: How to check if a value exists in hashmap?
You need to iterate through and check if such item exists. You can use `std::find_if() with a lambda or do that through a loop. If you do that quite often you may want to index values as well (see below)
Q2: How to iterate through all the values in a map and find the largest value or the smallest value ?
Again you iterate through container and find it or you can use std::max_element() or std::min_element() with a lambda as well. Though if you need to access values in sorted order you may consider to use boost::multimap which will allow to access data using hashed index by name and provide sorted or hashed index(es) for values, though you should be aware of a price of every index added.
answered Nov 23 '18 at 17:18
SlavaSlava
32.6k12865
add a comment |
For the second question, use:
std::map<std::string, int> foo = {{"John",100},{"Jeffrey",200},{"Krishna",147}};
std::cout << std::max_element(foo.begin(), foo.end(), (const auto& p1, const auto& p2){return p1.second < p2.second;})->first;
std::cout << std::min_element(foo.begin(), foo.end(), (const auto& p1, const auto& p2){return p1.second < p2.second;})->first;
Use an adapted lambda with std::find_if, you should be able to find also if a value exists in a map (or hash table).
answered Nov 23 '18 at 17:13
Matthieu BrucherMatthieu Brucher
15.9k32141
add a comment |
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2 Answers
2
active
oldest
votes
2 Answers
2
active
oldest
votes
active
oldest
votes
active
oldest
votes
Q1: How to check if a value exists in hashmap?
You need to iterate through and check if such item exists. You can use `std::find_if() with a lambda or do that through a loop. If you do that quite often you may want to index values as well (see below)
Q2: How to iterate through all the values in a map and find the largest value or the smallest value ?
Again you iterate through container and find it or you can use std::max_element() or std::min_element() with a lambda as well. Though if you need to access values in sorted order you may consider to use boost::multimap which will allow to access data using hashed index by name and provide sorted or hashed index(es) for values, though you should be aware of a price of every index added.
answered Nov 23 '18 at 17:18
SlavaSlava
32.6k12865
add a comment |
Q1: How to check if a value exists in hashmap?
You need to iterate through and check if such item exists. You can use `std::find_if() with a lambda or do that through a loop. If you do that quite often you may want to index values as well (see below)
Q2: How to iterate through all the values in a map and find the largest value or the smallest value ?
Again you iterate through container and find it or you can use std::max_element() or std::min_element() with a lambda as well. Though if you need to access values in sorted order you may consider to use boost::multimap which will allow to access data using hashed index by name and provide sorted or hashed index(es) for values, though you should be aware of a price of every index added.
answered Nov 23 '18 at 17:18
SlavaSlava
32.6k12865
add a comment |
Q1: How to check if a value exists in hashmap?
You need to iterate through and check if such item exists. You can use `std::find_if() with a lambda or do that through a loop. If you do that quite often you may want to index values as well (see below)
Q2: How to iterate through all the values in a map and find the largest value or the smallest value ?
Again you iterate through container and find it or you can use std::max_element() or std::min_element() with a lambda as well. Though if you need to access values in sorted order you may consider to use boost::multimap which will allow to access data using hashed index by name and provide sorted or hashed index(es) for values, though you should be aware of a price of every index added.
answered Nov 23 '18 at 17:18
SlavaSlava
32.6k12865
Q1: How to check if a value exists in hashmap?
You need to iterate through and check if such item exists. You can use `std::find_if() with a lambda or do that through a loop. If you do that quite often you may want to index values as well (see below)
Q2: How to iterate through all the values in a map and find the largest value or the smallest value ?
Again you iterate through container and find it or you can use std::max_element() or std::min_element() with a lambda as well. Though if you need to access values in sorted order you may consider to use boost::multimap which will allow to access data using hashed index by name and provide sorted or hashed index(es) for values, though you should be aware of a price of every index added.
answered Nov 23 '18 at 17:18
SlavaSlava
32.6k12865
answered Nov 23 '18 at 17:18
SlavaSlava
32.6k12865
answered Nov 23 '18 at 17:18
SlavaSlava
32.6k12865
answered Nov 23 '18 at 17:18
SlavaSlava
32.6k12865
32.6k12865
add a comment |
add a comment |
For the second question, use:
std::map<std::string, int> foo = {{"John",100},{"Jeffrey",200},{"Krishna",147}};
std::cout << std::max_element(foo.begin(), foo.end(), (const auto& p1, const auto& p2){return p1.second < p2.second;})->first;
std::cout << std::min_element(foo.begin(), foo.end(), (const auto& p1, const auto& p2){return p1.second < p2.second;})->first;
Use an adapted lambda with std::find_if, you should be able to find also if a value exists in a map (or hash table).
answered Nov 23 '18 at 17:13
Matthieu BrucherMatthieu Brucher
15.9k32141
add a comment |
For the second question, use:
std::map<std::string, int> foo = {{"John",100},{"Jeffrey",200},{"Krishna",147}};
std::cout << std::max_element(foo.begin(), foo.end(), (const auto& p1, const auto& p2){return p1.second < p2.second;})->first;
std::cout << std::min_element(foo.begin(), foo.end(), (const auto& p1, const auto& p2){return p1.second < p2.second;})->first;
Use an adapted lambda with std::find_if, you should be able to find also if a value exists in a map (or hash table).
answered Nov 23 '18 at 17:13
Matthieu BrucherMatthieu Brucher
15.9k32141
add a comment |
For the second question, use:
std::map<std::string, int> foo = {{"John",100},{"Jeffrey",200},{"Krishna",147}};
std::cout << std::max_element(foo.begin(), foo.end(), (const auto& p1, const auto& p2){return p1.second < p2.second;})->first;
std::cout << std::min_element(foo.begin(), foo.end(), (const auto& p1, const auto& p2){return p1.second < p2.second;})->first;
Use an adapted lambda with std::find_if, you should be able to find also if a value exists in a map (or hash table).
answered Nov 23 '18 at 17:13
Matthieu BrucherMatthieu Brucher
15.9k32141
For the second question, use:
std::map<std::string, int> foo = {{"John",100},{"Jeffrey",200},{"Krishna",147}};
std::cout << std::max_element(foo.begin(), foo.end(), (const auto& p1, const auto& p2){return p1.second < p2.second;})->first;
std::cout << std::min_element(foo.begin(), foo.end(), (const auto& p1, const auto& p2){return p1.second < p2.second;})->first;
Use an adapted lambda with std::find_if, you should be able to find also if a value exists in a map (or hash table).
answered Nov 23 '18 at 17:13
Matthieu BrucherMatthieu Brucher
15.9k32141
edited Nov 23 '18 at 17:21
answered Nov 23 '18 at 17:13
Matthieu BrucherMatthieu Brucher
15.9k32141
answered Nov 23 '18 at 17:13
Matthieu BrucherMatthieu Brucher
15.9k32141
answered Nov 23 '18 at 17:13
Matthieu BrucherMatthieu Brucher
15.9k32141
15.9k32141
add a comment |
add a comment |
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well, yes :) that's it
– OznOg
Nov 23 '18 at 17:07
2
en.cppreference.com/w/cpp/container/map
– Lightness Races in Orbit
Nov 23 '18 at 17:08
are you actually searching for the max or a random value?
– OznOg
Nov 23 '18 at 17:08
1
en.cppreference.com/w/cpp/algorithm
– Lightness Races in Orbit
Nov 23 '18 at 17:09
1
First you say map then you say hashmap - they are different make your mind
– Slava
Nov 23 '18 at 17:09