我试图编写一个函数 ReverseRange(struct Node **head, int x, int y)
,它将在给定的索引范围 int x
和 int y
中反转链表。我在 Reverse()
的条件之一中使用了先前定义的函数 ReverseRange()
,但它没有反转给定的列表,仅打印一个带有数据 'Q'
的节点。我不知道错误是在 Print()
或 Reverse()
或 ReverseRange()
或其他地方。请帮忙,谢谢。
#include <stdio.h>
#include <stdlib.h>
struct Node {
char data;
struct Node *next;
};
//insert data in the node
void Insert(struct Node **Head, char data) {
struct Node *temp = (struct Node *)malloc(sizeof(struct Node));
temp->data = data;
temp->next = *Head;
*Head = temp;
}
//find length of linked list
int LengthRec(struct Node *head) {
if (head == NULL)
return 0;
return 1 + LengthRec(head->next);
}
//Reverse a linked list when head is given;
void Reverse(struct Node **head) {
struct Node *prev = NULL;
struct Node *curr = *head;
struct Node *next = NULL;
while (curr != NULL) {
next = curr->next;
curr->next = prev;
prev = curr;
curr = next;
}
*head = prev;
}
//Reverse list in range x to y;
int ReverseRange(struct Node **H, int x, int y) {
struct Node *Head = *H;
if (Head == NULL)
return -1;
else if (Head->next == NULL)
return -1;
else if (x == y)
return -1;
else if (x > y)
return -1;
else if (LengthRec(Head) >= y) {
if (x == 1 && y == LengthRec(Head)) {
Reverse(&Head);
return 1;
}
/* NOTE::
Code is incomplete, because I found error before
the entire code is written,
*/
}
}
void Print(struct Node **H) {
struct Node *head = *H;
if (head == NULL) {
printf("Head=NULL");
return;
}
printf("\n %c", head->data);
while (head->next != NULL) {
head = head->next;
printf("\t%c", head->data);
}
}
int main() {
struct Node *Head = NULL;
Insert(&Head, 'Q');
Insert(&Head, 'W');
Insert(&Head, 'E');
Insert(&Head, 'R');
Insert(&Head, 'T');
Print(&Head);
Reverse(&Head);
Print(&Head);
ReverseRange(&Head, 1, 5);
Print(&Head);
}
输出:
T R E W Q
Q W E R T
Q
答案 0 :(得分:0)
Reverse
函数看起来不错,但应该使用 H
作为来自 ReverseRange()
的参数而不是局部变量 &Head
来调用它。
函数开头的一些显式测试对应于合法参数,不应返回错误值。
还要注意,您应该记录 x
和 y
的精确语义:在 C 中使用 1
来指定集合的第一个元素 {{1 }} 很常见。 0
似乎包含在内,这也不是惯用的,但与使用 y
作为第一个元素一致。
您的 1
函数效率非常低,对于很长的列表可能会导致堆栈溢出。使用循环而不是递归,因为此递归不是尾递归。
这是修改后的版本:
LengthRec
输出:
#include <stdio.h>
#include <stdlib.h>
struct Node {
char data;
struct Node *next;
};
//insert data in the node
void Insert(struct Node **Head, char data) {
struct Node *temp = (struct Node *)malloc(sizeof(struct Node));
temp->data = data;
temp->next = *Head;
*Head = temp;
}
//find length of linked list
int ListLength(const struct Node *head) {
int length = 0;
while (head != NULL) {
length++;
head = head->next;
}
return length;
}
//Reverse a linked list when head is given;
void Reverse(struct Node **head) {
struct Node *prev = NULL;
struct Node *curr = *head;
while (curr != NULL) {
struct Node *next = curr->next;
curr->next = prev;
prev = curr;
curr = next;
}
*head = prev;
}
//Reverse list in range x to y;
int ReverseRange(struct Node **H, int x, int y) {
int length = ListLength(*H);
if (x < 1 || x > length || x > y || y > length)
return -1;
if (x == y)
return 1;
if (x == 1 && y == length) {
Reverse(H);
return 1;
} else {
struct Node **head = H;
struct Node *prev = NULL;
struct Node *curr = *head;
struct Node *last;
while (x > 1) {
head = &curr->next;
curr = *head;
x--;
y--;
}
last = curr;
while (x <= y) {
struct Node *next = curr->next;
curr->next = prev;
prev = curr;
curr = next;
x++;
}
last->next = curr;
*head = prev;
return 1;
}
}
void Print(const char *msg, const struct Node *head) {
if (msg) {
printf("%s", msg);
}
if (head == NULL) {
printf("Head=NULL\n");
return;
}
printf("%c", head->data);
while (head->next != NULL) {
head = head->next;
printf("\t%c", head->data);
}
printf("\n");
}
int main() {
struct Node *Head = NULL;
Insert(&Head, 'E');
Insert(&Head, 'D');
Insert(&Head, 'C');
Insert(&Head, 'B');
Insert(&Head, 'A');
Print(" Initial list:\t", Head);
Reverse(&Head);
Print(" Reverse(&Head):\t", Head);
ReverseRange(&Head, 1, 5);
Print("ReverseRange(&Head,1,5):\t", Head);
ReverseRange(&Head, 1, 1);
Print("ReverseRange(&Head,1,1):\t", Head);
ReverseRange(&Head, 2, 4);
Print("ReverseRange(&Head,2,4):\t", Head);
return 0;
}