hashmap

问题 You might have come across someplace where it is mentioned that it is faster to find elements in hashmap/dictionary/table than list/array. My question is WHY? (inference so far I made: Why should it be faster, as far I see, in both data structure, it has to travel throughout till it reaches the required element) 回答1: Let’s reason by analogy. Suppose you want to find a specific shirt to put on in the morning. I assume that, in doing so, you don’t have to look at literally every item of

问题 You might have come across someplace where it is mentioned that it is faster to find elements in hashmap/dictionary/table than list/array. My question is WHY? (inference so far I made: Why should it be faster, as far I see, in both data structure, it has to travel throughout till it reaches the required element) 回答1: Let’s reason by analogy. Suppose you want to find a specific shirt to put on in the morning. I assume that, in doing so, you don’t have to look at literally every item of

问题 My objective is to create a map. It have reqid , name and lowest status number of a set as a key. Here set refers to rows belonging to a specific Reqid . The value of the map is an Arraylist which consists of all rows as objects of a specific id . public class MapKey { private Integer id; private String name; private Integer status; public MapKey(Integer id, String name,Integer status) { this.id = id; this.name = name; this.status=status; } @Override toString,hashCode,equals public class

问题 My objective is to create a map. It have reqid , name and lowest status number of a set as a key. Here set refers to rows belonging to a specific Reqid . The value of the map is an Arraylist which consists of all rows as objects of a specific id . public class MapKey { private Integer id; private String name; private Integer status; public MapKey(Integer id, String name,Integer status) { this.id = id; this.name = name; this.status=status; } @Override toString,hashCode,equals public class

问题 I am trying to Test a method but it has a global variable which is null, Please guide me so I can assign value to global variable i.e. a Map My Junit: public class ErrorTest { @Mock private DataSource db; @Mock private JdbcTemplate jdbcTemplate; @InjectMocks private RateServiceImpl rateService = new RateServiceImpl(); @Mock private RaterDao raterDao; @Resource private MessageSource msg ; @Mock Map<String, StringAttribute> errorMap = new HashMap<String, StringAttribute>(); @Before public void

问题 Can anyone assist me with an alternative to if then else statements for control flow? Or advise on a good article? From what I've seen, some use mapping or enums. Trouble I'm having is that I have multiple conditions i.e. if (condition1 && condition2 && condition3)... and I need to do this for several permutations and all 3 variables need to be validated. Please can someone point me in the right direction? else if (String.Utils.isNotEmpty(payload.getKeyChange2TokenNumber()) && String.Utils

问题 Can anyone assist me with an alternative to if-then-else statements for control flow? Or advise on a good article? From what I've seen, some use mapping or enums. Trouble I'm having is that I have multiple conditions i.e. if (condition1 && condition2 && condition3)... and I need to do this for several permutations and all 3 variables need to be validated. Please can someone point me in the right direction? else if (String.Utils.isNotEmpty(payload.getKeyChange2TokenNumber()) && String.Utils

问题 The built in maps and sets in C++ libraries (including unordered_map and multimap) requires that the find function (used to lookup a specific element) utilize an iterator for traversing the elements. The C++ reference site claims that looking up elements using these data structures takes on average constant time, much like a regular hash table. But wouldn't an iterator have to traverse the entire list, making this O(n) time on average, before finding the element? 回答1: You statement are no

问题 I need a 'List' or 'Map',... of object A. This list will be added from another ArrayList. Object A is considered to be equal to another when id parameter of A equals. My problem is I only want add an object that does not exist in my List. I wonder between the two alternatives for implementation. Using ArrayList or HashMap 1. ArrayList: for (A a: source) {if (! (a in ArrayList)) addToArrayList();} 2. HashMap <id, A> for (A a: source) {hasmap.put (a.id, a)} Which will give better speed to add a

问题 I've just started learning about hash tables and I understand how to insert but not how to search. These are the algorithms I'll be basing this question off: Hashing the key int Hash (int key) { return key % 10; //table has a max size of 10 } Linear probing for collision resolution. Suppose I call insert twice with the keys 1, 11, and 21. This would return slot 1 for all 3 keys. After collision resolution the table would have the values 1, 11, and 21 at slots 1, 2, and 3. This is what I