摘要: 静态链表有助于理解操作系统空间分配机制, 遗憾的是, 多数人没写这个代码. 强烈建议硬杠一下. 毕竟这是学霸与学渣的重要分界线.
1. 代码 (2022 版)
先上代码, 再说废话.
#include <stdio.h>
#include <malloc.h>
#define DEFAULT_SIZE 5
typedef struct StaticLinkedNode{
char data;
int next;
} *NodePtr;
typedef struct StaticLinkedList{
NodePtr nodes;
int* used;
} *ListPtr;
/**
* Initialize the list with a header.
* @return The pointer to the header.
*/
ListPtr initLinkedList(){
// The pointer to the whole list space.
ListPtr tempPtr = (ListPtr)malloc(sizeof(StaticLinkedList));
// Allocate total space.
tempPtr->nodes = (NodePtr)malloc(sizeof(struct StaticLinkedNode) * DEFAULT_SIZE);
tempPtr->used = (int*)malloc(sizeof(int) * DEFAULT_SIZE);
// The first node is the header.
tempPtr->nodes[0].data = '\0';
tempPtr->nodes[0].next = -1;
// Only the first node is used.
tempPtr->used[0] = 1;
for (int i = 1; i < DEFAULT_SIZE; i ++){
tempPtr->used[i] = 0;
}// Of for i
return tempPtr;
}// Of initLinkedList
/**
* Print the list.
* @param paraListPtr The pointer to the list.
*/
void printList(ListPtr paraListPtr){
int p = 0;
while (p != -1) {
printf("%c", paraListPtr->nodes[p].data);
p = paraListPtr->nodes[p].next;
}// Of while
printf("\r\n");
}// Of printList
/**
* Insert an element to the given position.
* @param paraListPtr The position of the list.
* @param paraChar The given char.
* @param paraPosition The given position.
*/
void insertElement(ListPtr paraListPtr, char paraChar, int paraPosition){
int p, q, i;
// Step 1. Search to the position.
p = 0;
for (i = 0; i < paraPosition; i ++) {
p = paraListPtr->nodes[p].next;
if (p == -1) {
printf("The position %d is beyond the scope of the list.\r\n", paraPosition);
return;
}// Of if
} // Of for i
// Step 2. Construct a new node.
for (i = 1; i < DEFAULT_SIZE; i ++){
if (paraListPtr->used[i] == 0){
// This is identical to malloc.
printf("Space at %d allocated.\r\n", i);
paraListPtr->used[i] = 1;
q = i;
break;
}// Of if
}// Of for i
if (i == DEFAULT_SIZE){
printf("No space.\r\n");
return;
}// Of if
paraListPtr->nodes[q].data = paraChar;
// Step 3. Now link.
printf("linking\r\n");
paraListPtr->nodes[q].next = paraListPtr->nodes[p].next;
paraListPtr->nodes[p].next = q;
}// Of insertElement
/**
* Delete an element from the list.
* @param paraHeader The header of the list.
* @param paraChar The given char.
*/
void deleteElement(ListPtr paraListPtr, char paraChar){
int p, q;
p = 0;
while ((paraListPtr->nodes[p].next != -1) && (paraListPtr->nodes[paraListPtr->nodes[p].next].data != paraChar)){
p = paraListPtr->nodes[p].next;
}// Of while
if (paraListPtr->nodes[p].next == -1) {
printf("Cannot delete %c\r\n", paraChar);
return;
}// Of if
q = paraListPtr->nodes[p].next;
paraListPtr->nodes[p].next = paraListPtr->nodes[paraListPtr->nodes[p].next].next;
// This statement is identical to free(q)
paraListPtr->used[q] = 0;
}// Of deleteElement
/**
* Unit test.
*/
void appendInsertDeleteTest(){
// Step 1. Initialize an empty list.
ListPtr tempList = initLinkedList();
printList(tempList);
// Step 2. Add some characters.
insertElement(tempList, 'H', 0);
insertElement(tempList, 'e', 1);
insertElement(tempList, 'l', 2);
insertElement(tempList, 'l', 3);
insertElement(tempList, 'o', 4);
printList(tempList);
// Step 3. Delete some characters (the first occurrence).
printf("Deleting 'e'.\r\n");
deleteElement(tempList, 'e');
printf("Deleting 'a'.\r\n");
deleteElement(tempList, 'a');
printf("Deleting 'o'.\r\n");
deleteElement(tempList, 'o');
printList(tempList);
insertElement(tempList, 'x', 1);
printList(tempList);
}// Of appendInsertDeleteTest
/**
* The entrance.
*/
void main(){
appendInsertDeleteTest();
}// Of main
2. 运行结果
Space at 1 allocated.
linking
Space at 2 allocated.
linking
Space at 3 allocated.
linking
Space at 4 allocated.
linking
No space.
Hell
Deleting 'e'.
Deleting 'a'.
Cannot delete a
Deleting 'o'.
Cannot delete o
Hll
Space at 2 allocated.
linking
Hxll
Press any key to continue
3. 代码说明
- nodes 存储节点, used 存储空间使用情况, 0 表示空闲, 1 表示被占用.
- next 是一个整数, 表示相对地址. 在操作系统中, 应该是绝对地址.
- 这里用 -1 表示 NULL.
- nodes[0] 永远存储头节点.
- 并没考虑多个链表共享同一片空间的情况, 但这是真实操作系统需要面对的.
- paraListPtr->nodes[paraListPtr->nodes[p].next].data 这种代码有一点点复杂, 懂了就好办. 这个代码的调拭也就 10 分钟.
欢迎留言讨论.