I'm currently making a tic-tac-toe program with AI and i'm having a bit of a trouble translating this line of code (python) :
RANKS = dict([(4,3), # center = 3 (0,2),(2,2),(6,2),(8,2), # corners = 2 (1,1),(3,1),(5,1),(7,1)]) # sides = 1into C++
any suggestions?
25 Answers
The closest match in C++ would be an std::unordered_map<int, int>. This is a hash table mapping int keys to int values.
#include <unordered_map>
std::unordered_map<int, int> RANKS = { { 4, 3 }, { 0, 2 }, { 2, 2 }, { 6, 2 }, { 8, 2 }, { 1, 1 }, { 3, 1 }, { 5, 1 }, { 7, 1 }
};You can access elements using operator[], for example
std::cout << RANKS[0] << std::endl; // prints "2"Note that the C++ standard library also has the std::map class template, which allows you to create a similar but ordered look-up table std::map<int, int>, with logarithmic look-up and insertion complexity. But python dicts are hash tables, so unordered_map is a closer match in terms of behaviour.
You could use a map or unordered_map for this (and they'd work fine) but given that your keys are a dense set of integers (I.e. all the integers from 0 to N) there are better choices.
I'd probably use an std::array instead. It would look something like this:
std::array <char, 9> vals = { 2, 1, 2, 1, 3, 1, 2, 1, 2 };This gives pretty much the same syntax and observable behavior, but will typically save quite a bit of memory and probably CPU time as well.
In C++ this would be a std::unordered_map
#include <unordered_map>
std::unordered_map<int, int> dict
{ { { 4, 3 }, { 0, 2 }, { 2, 2 }, { 6, 2 }, { 8, 2 }, { 1, 1 }, { 3, 1 }, { 5, 1 }, { 7, 1 } }
};The C++ equivalent of Python's dict is std::map. To initialize a map using a similar syntax, do this:
std::map<int,int> myMap = {{4,3}, # center = 3 {0,2},{2,2},{6,2},{8,2}, # corners = 2 {1,1},{3,1},{5,1},{7,1}}; # sides = 1Note that this needs C++11.
If you cannot use C++11, turn to map_list_of in Boost.Assign. The example from their page is:
using namespace boost::assign; // bring 'map_list_of()' into scope
std::map<int,int> next = map_list_of(1,2)(2,3)(3,4)(4,5)(5,6);Although a "language equivalent" might me something like an std::unordered_map your use case may be more efficiently served with a straight array:
int RANKS[] = {2, 1, 2, 1, 3, 1, 2, 1, 2};
