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问题 Closed . This question needs to be more focused. It is not currently accepting answers. Want to improve this question? Update the question so it focuses on one problem only by editing this post. Closed 2 years ago . I have confused with lists, tuples, sets and dictionaries someone give me clear cut idea . Give me the difference from your understanding don't give the text book definitions. 回答1: A list is a sequence of elements in a specific order. You can access elements with a numerical index

问题 I need a sorted and indexed container. I want to build it based on std:set or std::vector. By using set, I need expensive std::distance to calculate the index of its element. By using vector, I know adding or deleting an element is expensive. Let's say my element is a pointer (small object). I know two operations' complexity is the same. But which one is faster? Thanks. 回答1: If you need a data structure that supports sorted order and lookup by index, you should definitely look into the order

问题 I need a sorted and indexed container. I want to build it based on std:set or std::vector. By using set, I need expensive std::distance to calculate the index of its element. By using vector, I know adding or deleting an element is expensive. Let's say my element is a pointer (small object). I know two operations' complexity is the same. But which one is faster? Thanks. 回答1: If you need a data structure that supports sorted order and lookup by index, you should definitely look into the order

问题 So we get a new set of strings, and we have one as map Keys. And we want to do one way set_difference (note - not set_symmetric_difference). So currently I have such ugly code like: std::map<std::string, boost::shared_ptr<some_class> > _ds; std::set<std::string> compare_and_clean(std::set<std::string> &new_) { std::set<std::string> result; std::set<std::string> old; for (std::map<std::string, std::string>::iterator mi = _ds.begin(); mi != _ds.end(); ++mi) old.insert(mi->first); std::set

问题 I have to use a HashSet where a lot of duplicate value may be inserted. But I want to preserve the earlier data inserted in the hash when a later insertion makes the duplicate. To examine this I have write the following code and insert many duplicate value, but it doesn't satisfy me. Please see the code below - import java.util.HashSet; import java.util.Set; public class SetTest { private static Set<Student> studentSet = new HashSet<Student>(); private static Student s1, s2, s3, s4, s5, s6,

问题 I have to use a HashSet where a lot of duplicate value may be inserted. But I want to preserve the earlier data inserted in the hash when a later insertion makes the duplicate. To examine this I have write the following code and insert many duplicate value, but it doesn't satisfy me. Please see the code below - import java.util.HashSet; import java.util.Set; public class SetTest { private static Set<Student> studentSet = new HashSet<Student>(); private static Student s1, s2, s3, s4, s5, s6,

问题 I'm trying to prove that type-level function Union is associative, but I'm not sure how it should be done. I proved right identity and associativity laws for type-level append function and right identity for union: data SList (i :: [k]) where SNil :: SList '[] SSucc :: SList t -> SList (h ': t) appRightId :: SList xs -> xs :~: (xs :++ '[]) appRightId SNil = Refl appRightId (SSucc xs) = case appRightId xs of Refl -> Refl appAssoc :: SList xs -> Proxy ys -> Proxy zs -> (xs :++ (ys :++ zs)) :~:

问题 I have a dict like this: (100002: 'APPLE', 100004: 'BANANA', 100005: 'CARROT') I am trying to make my dict have ints for the keys (as it does now) but have sets for the values (rather than strings as it is now.) My goal is to be able to read from a .csv file with one column for the key (an int which is the item id number) and then columns for things like size, shape, and color. I want to add this information into my dict so that only the information for keys already in dict are added. My goal

问题 Given an array ['a', 'b', 'c', 'd', 'e', 'f'] , how would I get a list of all subsets containing two, three, and four elements? I'm quite new to Ruby (moving from C#) and am not sure what the 'Ruby Way' would be. 回答1: Check out Array#combination Then something like this: 2.upto(4) { |n| array.combination(n) } 回答2: Tweaking basicxman's a little bit: 2.upto(4).flat_map { |n| array.combination(n).to_a } #=> [["a", "b"], ["a", "c"], ["a", "d"], ..., ["c", "d", "e", "f"]] 来源： https://stackoverflow

问题 Here is my code: <?php class SampleClass { public function __get($name){ echo "get called"; echo $name; } public function __set($name, $value) { echo "set called"; } } ?> And my index file: $object = new SampleClass(); $object->color = "black"; echo $object->color; If I run this code as it is, here is the output: set calledget calledcolor However if I comment out public function __set($name, $value) { echo "set called"; } the part above (only this part), then the output will be: black So what