LeetCode 138 Copy List with Random Pointer (C++, Python)

-
A linked list is given such that each node contains an additional random pointer which could point to any node in the list or null.
Return a deep copy of the list.
Solution C++


 1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
/**
 * Definition for singly-linked list with a random pointer.
 * struct RandomListNode {
 *     int label;
 *     RandomListNode *next, *random;
 *     RandomListNode(int x) : label(x), next(NULL), random(NULL) {}
 * };
 */
class Solution {
public:
    RandomListNode *copyRandomList(RandomListNode *head) {
        unordered_map<RandomListNode*, RandomListNode*> um; 
        um[NULL] = NULL;
        RandomListNode* node = head;
        RandomListNode* copyhead = NULL;
        while (node) {
            RandomListNode* copy = new RandomListNode(node->label);
            if (copyhead == NULL) copyhead = copy;
            copy->next = node->next;
            copy->random = node->random;
            um[node] = copy;
            node = node->next;
        }
        node = copyhead;
        while (node) {
            node->next = um[node->next];
            node->random = um[node->random];
            node = node->next;
        }
        return copyhead;
    }
};
Solution


 1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
# Definition for singly-linked list with a random pointer.
# class RandomListNode:
#     def __init__(self, x):
#         self.label = x
#         self.next = None
#         self.random = None

class Solution:
    # @param head, a RandomListNode
    # @return a RandomListNode
    def copyRandomList(self, head):
        nodemap = {None:None}
        node = head
        copyhead = None
        while node:
            copy = RandomListNode(node.label)
            if copyhead is None:
                copyhead = copy
            nodemap[node] = copy
            copy.next = node.next
            copy.random = node.random
            node = node.next
        
        node = copyhead
        while node:
            node.next = nodemap[node.next]
            node.random = nodemap[node.random]
            node = node.next
        return copyhead

Popular posts from this blog

How Django Works (4) URL Resolution

-
Image
Why We Need URL Resolution Theoretically, we could write a single function to process all incoming HTTP requests. It would work well for very simple websites. For any real websites, it would be much more appropriate to categorize HTTP requests based on their URLs and process them separately in different handlers. For example, BASEURL/polls/ would be an application for polls whereas BASEURL/blogs/ would be an application for blogs. This way, different URLs can be considered different logic applications, so we can think of websites in terms of logic applications – a higher level of abstraction that HTTP request/response pairs. Fortunately, many modern web frameworks come default with mechanisms that do the categorization of HTTP requests based on URIs, which spares us the effort of having to reinvent the wheel.   Django's URL Resolution The official Django document has following description about how Django processes a request. https://docs.djangoproject.com/en/1.8/topic...
Read more

Python Class Method and Class Only Method

-
In this post, I will be discussing Python method especially class method. Example class Foo : def bar_inst ( self ): print ( self , "This is bar_inst" ) @staticmethod def bar_static (): print ( "This is bar_static" ) @classmethod def bar_class (cls): print (cls, "This is bar_class" ) >>> foo = Foo() >>> foo.bar_inst <bound method Foo.bar_inst of <test.Foo object at 0x025A0EB0>> >>> foo.bar_static <function Foo.bar_static at 0x025A34F8> >>> foo.bar_class <bound method type.bar_class of <class 'test.Foo'>> foo.bar_static just returns a function object as if bar_static were defined outside of class. (In Python 2, it would return an unbound method; Python 3 has removed the concept of unbound methods. So a function is either a bound method or a regular function object) How It Works -- Descriptor  Every ...
Read more

How Django works (3): Testing Server and Static Files Serving

-
How Django Handles Static Files By default, Django installs an Application django.contrib.staticfiles, which is responsible for handling requests to files under STATIC_URL.   INSTALLED_APPS = ( 'django.contrib.admin' , 'django.contrib.auth' , 'django.contrib.contenttypes' , 'django.contrib.sessions' , 'django.contrib.messages' , 'django.contrib.staticfiles' , 'polls' , ) STATIC_URL = '/static/' This method is grossly inefficient and probably insecure, so it is unsuitable for production. https://docs.djangoproject.com/en/1.8/howto/static-files/deployment/ How staticfiles App Works Based on the first blog of Django series, Django interacts with web servers by providing a callable application that conforms to WSGI specification. 1 2 3 4 5 class WSGIHandler (base . BaseHandler): initLock = Lock() request_class = WSGIRequest def __call__ ( self , environ, start_...
Read more