自组织列表：移至最前方法

自组织列表是重新组织或重新排列自身以提高性能的列表。在一个简单的列表中，以顺序方式查找要搜索的项目，该方式给出了O(n)的时间复杂度。但是在实际情况下，并非所有项目都会被频繁搜索，并且在大多数情况下，只有很少的项目会被多次搜索。

因此，自组织列表使用此属性(也称为参考位置)将最常用的项目放在列表的顶部。这增加了在列表的开头找到该项目的可能性，并且那些很少使用的元素被推到列表的后面。

在“移至最前方法”中，最近搜索的项目将移至列表的最前面。因此，此方法很容易实现，但也将不经常搜索的项目移到最前面。将不频繁搜索的项目移到最前面是此方法的一大缺点，因为它会影响访问时间。

例子：

Input :   list : 1, 2, 3, 4, 5, 6
          searched: 4 
Output :  list : 4, 1, 2, 3, 5, 6

Input :   list : 4, 1, 2, 3, 5, 6
          searched : 2
Output :  list : 2, 4, 1, 3, 5, 6

// CPP Program to implement self-organizing list
// using move to front method
#include 
using namespace std;
  
// structure for self organizing list
struct self_list {
    int value;
    struct self_list* next;
};
  
// head and rear pointing to start and end of list resp.
self_list *head = NULL, *rear = NULL;
  
// function to insert an element
void insert_self_list(int number)
{
    // creating a node
    self_list* temp = (self_list*)malloc(sizeof(self_list));
  
    // assigning value to the created node;
    temp->value = number;
    temp->next = NULL;
  
    // first element of list
    if (head == NULL)
        head = rear = temp;
  
    // rest elements of list
    else {
        rear->next = temp;
        rear = temp;
    }
}
  
// function to search the key in list
// and re-arrange self-organizing list
bool search_self_list(int key)
{
    // pointer to current node
    self_list* current = head;
  
    // pointer to previous node
    self_list* prev = NULL;
  
    // searching for the key
    while (current != NULL) {
  
        // if key found
        if (current->value == key) {
  
            // if key is not the first element
            if (prev != NULL) {
  
                /* re-arranging the elements */
                prev->next = current->next;
                current->next = head;
                head = current;
            }
            return true;
        }
        prev = current;
        current = current->next;
    }
  
    // key not found
    return false;
}
  
// function to display the list
void display()
{
    if (head == NULL) {
        cout << "List is empty" << endl;
        return;
    }
  
    // temporary pointer pointing to head
    self_list* temp = head;
    cout << "List: ";
  
    // sequentially displaying nodes
    while (temp != NULL) {
        cout << temp->value;
        if (temp->next != NULL)
            cout << " --> ";
  
        // incrementing node pointer.
        temp = temp->next;
    }
    cout << endl  << endl;
}
  
// Driver Code
int main()
{
    /* inserting five values */
    insert_self_list(1);
    insert_self_list(2);
    insert_self_list(3);
    insert_self_list(4);
    insert_self_list(5);
  
    // Display the list
    display();
  
    // search 4 and if found then re-arrange
    if (search_self_list(4))
        cout << "Searched: 4" << endl;
    else
        cout << "Not Found: 4" << endl;
  
    // Display the list
    display();
  
    // search 2 and if found then re-arrange
    if (search_self_list(2))
        cout << "Searched: 2" << endl;
    else
        cout << "Not Found: 2" << endl;
    display();
  
    return 0;
}

输出：

List: 1 --> 2 --> 3 --> 4 --> 5

Searched: 4
List: 4 --> 1 --> 2 --> 3 --> 5

Searched: 2
List: 2 --> 4 --> 1 --> 3 --> 5