从单遍遍URL的长列表中查找最后一个唯一的URL

给定很长的URL列表，找出最后一个唯一的URL。只允许遍历所有URL。

例子：

Input:
https://www.geeksforgeeks.org
http://quiz.geeksforgeeks.org 
http://qa.geeksforgeeks.org 
https://practice.geeksforgeeks.org 
https://ide.geeksforgeeks.org
http://www.contribute.geeksforgeeks.org  
http://quiz.geeksforgeeks.org 
https://practice.geeksforgeeks.org 
https://ide.geeksforgeeks.org 
http://quiz.geeksforgeeks.org 
http://qa.geeksforgeeks.org 
https://practice.geeksforgeeks.org

Output:
http://www.contribute.geeksforgeeks.org

通过将Trie与双链表一起使用，我们可以一次遍历解决此问题(我们可以在O(1)时间插入和删除)。想法是将所有URL都一一插入到Trie中，并检查是否重复。要知道我们以前是否遇到过URL，我们需要将每个URL的最后一个节点标记为叶节点。如果是第一次遇到URL，则将其插入到双向链接列表中，并在该trie的叶子节点中的链接列表中维护指向该节点的指针。如果遇到的URL已经存在于Trie中，并且在链接列表中具有指向该URL的指针，则从链接列表中删除该节点，并将其在Trie中的指针设置为null。处理完所有URL后，链接列表将仅包含不同的URL，并且链接列表开头的节点将是最后一个唯一URL。

// C++ program to print distinct URLs using Trie
// and Doubly Linked List
#include 
using namespace std;
  
// Alphabet size (# of symbols)
const int ALPHABET_SIZE = 256;
  
// A linked list node
struct DLLNode
{
    string data;
    DLLNode* next, * prev;
};
  
// trie node
struct TrieNode
{
    TrieNode* children[ALPHABET_SIZE];
  
    // isLeaf is true if the node represents
    // end of a word
    bool isLeaf;
  
    DLLNode* LLptr;
};
  
/* Given a reference (pointer to pointer) to the
   head of a list and an int, inserts a new node
   on the front of the list. */
void push(DLLNode*& head_ref, string new_data)
{
    DLLNode* new_node = new DLLNode;
  
    // put in the data
    new_node->data = new_data;
  
    // Make next of new node as head and previous
    // as NULL
    new_node->next = (head_ref);
    new_node->prev = NULL;
  
    // change prev of head node to new node
    if(head_ref != NULL)
        head_ref->prev = new_node;
  
    // move the head to point to the new node
    head_ref = new_node;
}
  
/* Function to delete a node in a Doubly Linked List.
   head_ref --> pointer to head node pointer.
   del  -->  pointer to node to be deleted. */
void deleteNode(DLLNode*& head_ref, DLLNode* del)
{
    // base case
    if (head_ref == NULL || del == NULL)
        return;
  
    // If node to be deleted is head node
    if (head_ref == del)
        head_ref = del->next;
  
    // Change next only if node to be deleted is
    // NOT the last node
    if (del->next != NULL)
        del->next->prev = del->prev;
  
    // Change prev only if node to be deleted is
    // NOT the first node
    if (del->prev != NULL)
        del->prev->next = del->next;
  
    // Finally, free the memory occupied by del
    delete(del);
    return;
}
  
// Returns new trie node (initialized to NULLs)
TrieNode* getNewTrieNode(void)
{
    TrieNode* pNode = new TrieNode;
  
    if (pNode)
    {
        pNode->isLeaf = false;
  
        for (int i = 0; i < ALPHABET_SIZE; i++)
            pNode->children[i] = NULL;
  
        pNode->LLptr = NULL;
    }
  
    return pNode;
}
  
// If not present, inserts key into trie
// If the key is prefix of trie node, just marks leaf node
void insert(TrieNode* root, string key, DLLNode*& head)
{
    int index;
    TrieNode* pCrawl = root;
  
    for (int level = 0; level < key.length(); level++)
    {
        index = int(key[level]);
        if (!pCrawl->children[index])
            pCrawl->children[index] = getNewTrieNode();
  
        pCrawl = pCrawl->children[index];
    }
  
    if (pCrawl->isLeaf)
    {
        // cout << "Duplicate Found " << key << endl;
        // delete from linked list
        if (pCrawl->LLptr)
            deleteNode(head, pCrawl->LLptr);
        pCrawl->LLptr = NULL;
    }
    else
    {
        // mark last node as leaf
        pCrawl->isLeaf = true;
  
        // insert to linked list
        push(head, key);
        pCrawl->LLptr = head;
    }
}
  
// Driver function
int main()
{
    string urls[] = {
        "https://www.geeksforgeeks.org",
        "http://www.contribute.geeksforgeeks.org",
        "http://quiz.geeksforgeeks.org",
        "http://qa.geeksforgeeks.org",
        "https://practice.geeksforgeeks.org",
        "https://ide.geeksforgeeks.org",
        "http://quiz.geeksforgeeks.org",
        "https://practice.geeksforgeeks.org",
        "https://ide.geeksforgeeks.org",
        "http://quiz.geeksforgeeks.org",
        "http://qa.geeksforgeeks.org",
        "https://practice.geeksforgeeks.org"
        };
  
    TrieNode* root = getNewTrieNode();
  
    // Start with the empty list
    DLLNode* head = NULL;
    int n = sizeof(urls)/sizeof(urls[0]);
  
    // Construct Trie from given URLs
    for (int i = 0; i < n; i++)
        insert(root, urls[i], head);
  
    // head of linked list will point to last
    // distinct URL
    cout << head->data << endl;
  
    return 0;
}

输出：

http://www.contribute.geeksforgeeks.org