XOR linked list

XOR linked list 是为了解决双向链表两个指针占用空间的问题

XOR：异或，数学符号 “^”

XOR linked list 是将节点的previous 和 next 通过XOR算出结果保存在 npx（变量，起什么名字都无所谓）。这样就可以节省一个指针的空间，若果需要previous，previous = npx ^ next;

 1 #include<stdio.h>
 2 #include<stdlib.h>
 3 #include<inttypes.h>
 4 
 5 struct node{
 6     int data;
 7     struct node * npx;
 8 };
 9 
10 struct node * XOR(struct node * pre, struct node * next)
11 {
12     return (struct node *)((uintptr_t)(pre) ^ (uintptr_t)(next));
13 }
14 
15 void insert(struct node ** head_ref, int data)
16 {
17     struct node * new_node = (struct node *)malloc(sizeof(struct node));
18     new_node->data = data;
19     new_node->npx = XOR(NULL, (*head_ref));
20 
21     if(NULL != (*head_ref))
22     {
23         struct node * next = XOR(NULL, (*head_ref)->npx);
24         (*head_ref)->npx = XOR(new_node, next);
25     }
26 
27     (*head_ref) = new_node;
28 }
29 void printXORlinkedlist(struct node * head_ref)
30 {
31     struct node * current = head_ref;
32     struct node * pre = NULL;
33     struct node * next;
34 
35     while(NULL != current)
36     {
37         printf("%d  ", current->data);
38 
39         next = XOR(current->npx, pre);
40 
41         pre = current;
42         current = next;
43     }
44 }
45 int main(void)
46 {
47     struct node * head = NULL;
48 
49     insert(&head, 0);
50     insert(&head, 1);
51     insert(&head, 2);
52     insert(&head, 3);
53 
54     printXORlinkedlist(head);
55     return 0;
56 }

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