PL/I 语言链表的创建、插入与删除实战
链表是一种常见的数据结构，它由一系列节点组成，每个节点包含数据和指向下一个节点的指针。PL/I（Programming Language One）是一种高级程序设计语言，它支持多种数据结构和算法的实现。在本篇文章中，我们将通过PL/I语言来实战链表的创建、插入与删除操作。
一、链表的基本概念
在PL/I中，链表是一种动态数据结构，它允许我们在运行时动态地创建和删除节点。链表由以下部分组成：
- 节点（Node）：链表的基本单元，包含数据和指向下一个节点的指针。
- 链表头（Head）：指向链表第一个节点的指针。
- 链表尾（Tail）：指向链表最后一个节点的指针。
二、链表的创建
我们需要定义一个节点结构体，然后创建一个链表头节点。
pl/i
IDENTIFICATION DIVISION.
PROGRAM-ID. CREATE-LINKED-LIST.
DATA DIVISION.
WORKING-STORAGE SECTION.
01 NODE-STRUCTURE.
05 DATA-FIELD PIC X(20).
05 NEXT-NODE-POINTER USAGE IS POINTER.
01 HEAD-POINTER USAGE IS POINTER.
01 TEMP-POINTER USAGE IS POINTER.
PROCEDURE DIVISION.
PERFORM INITIALIZE-LINKED-LIST
PERFORM INSERT-NODE-USING "First Node"
PERFORM INSERT-NODE-USING "Second Node"
PERFORM INSERT-NODE-USING "Third Node"
PERFORM PRINT-LINKED-LIST
STOP RUN.
INITIALIZE-LINKED-LIST.
SET HEAD-POINTER TO NULL.
INSERT-NODE-USING.
ACCEPT DATA-FIELD FROM ARGUMENT-VALUE.
PERFORM CREATE-NEW-NODE
PERFORM INSERT-NEW-NODE.
CREATE-NEW-NODE.
PERFORM ALLOCATE-NODE-USING NODE-STRUCTURE
SET DATA-FIELD OF NODE-STRUCTURE TO DATA-FIELD
SET NEXT-NODE-POINTER OF NODE-STRUCTURE TO NULL.
INSERT-NEW-NODE.
IF HEAD-POINTER IS NULL
SET HEAD-POINTER TO NODE-STRUCTURE
ELSE
SET TEMP-POINTER TO HEAD-POINTER
PERFORM UNTIL NEXT-NODE-POINTER OF TEMP-POINTER IS NULL
SET TEMP-POINTER TO NEXT-NODE-POINTER OF TEMP-POINTER
END-PERFORM
SET NEXT-NODE-POINTER OF TEMP-POINTER TO NODE-STRUCTURE.
PRINT-LINKED-LIST.
SET TEMP-POINTER TO HEAD-POINTER
PERFORM UNTIL TEMP-POINTER IS NULL
DISPLAY DATA-FIELD OF NODE-STRUCTURE
SET TEMP-POINTER TO NEXT-NODE-POINTER OF TEMP-POINTER
END-PERFORM.
三、链表的插入
在链表中插入新节点通常有以下几种情况：
1. 在链表头部插入。
2. 在链表尾部插入。
3. 在链表中间某个位置插入。
以下是一个在链表尾部插入新节点的示例：
pl/i
INSERT-NODE-AT-TAIL.
PERFORM CREATE-NEW-NODE
IF HEAD-POINTER IS NULL
SET HEAD-POINTER TO NODE-STRUCTURE
ELSE
SET TEMP-POINTER TO HEAD-POINTER
PERFORM UNTIL NEXT-NODE-POINTER OF TEMP-POINTER IS NULL
SET TEMP-POINTER TO NEXT-NODE-POINTER OF TEMP-POINTER
END-PERFORM
SET NEXT-NODE-POINTER OF TEMP-POINTER TO NODE-STRUCTURE.
四、链表的删除
删除链表中的节点通常有以下几种情况：
1. 删除链表头部节点。
2. 删除链表尾部节点。
3. 删除链表中间某个位置的节点。
以下是一个删除链表头部节点的示例：
pl/i
DELETE-NODE-AT-HEAD.
IF HEAD-POINTER IS NOT NULL
SET TEMP-POINTER TO HEAD-POINTER
SET HEAD-POINTER TO NEXT-NODE-POINTER OF TEMP-POINTER
DEALLOCATE TEMP-POINTER
ELSE
DISPLAY "Linked list is empty."
五、总结
通过以上示例，我们了解了如何在PL/I语言中创建、插入和删除链表。链表是一种灵活且强大的数据结构，在许多应用场景中都有广泛的应用。在实际编程中，我们可以根据具体需求对链表进行扩展和优化。
本文以3000字左右的篇幅，详细介绍了PL/I语言链表的创建、插入与删除操作。希望对您在学习和应用PL/I语言链表时有所帮助。
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