C 中的链表（中间插入）

Question

Write a program containing a linked list of integers that allows you to duplicate X element next to the X element in the list (X is given by user). Example: List:1,4,3,2,5,3,7; X=3. Resulting list: 1,4,3,3,2,5,3,3,7.

这就是我需要解决的问题，但我尝试了一切。链接列表是我没有想到的东西。我知道如何在结尾和开头添加一个数字，但在这个问题中我什至不知道从哪里开始。这就是我到目前为止所拥有的：

#include <stdio.h>
#include <stdlib.h>

typedef struct node{
  int x;
  struct node *next;
}Node;

// Check if the list is empty
int empty(Node *list){
  if(list->next == NULL)
    return 1;
  else
    return 0;
}

// Insert a number
void insert(Node *list){
  Node *newn=(Node *) malloc(sizeof(Node));
  printf("\nNumber: "); 
  scanf("%d", &newn->x);
  newn->next = NULL;

  if(empty(list))
    list->next=newn;
  else{
    Node *aux = list->next;
    while(aux->next != NULL){
      aux = aux->next;
    }
    aux->next = newn;
  }
}

// Print the list
void print(Node *list){
  Node *next = list;
  int i=1;

  printf("\n");
  if(empty(list)){
    printf("EMPTY!\n");
  }else{
    list = list->next;
    while(list!=NULL){
      printf("NUMBER [%2d]: %d\n", i++, list->x);
      list = list->next;
    }
  }
}

// Duplicate X values in the list
void duplicate(Node *lista){

}

int main(void) {
  Node *list = (Node*)malloc(sizeof(Node));

  int op, val;

  do{
    printf("\n1 - Insert\n");
    printf("2 - Print\n");
    printf("3 - Duplicate X\n");
    printf("5 - Close\n");
    printf("OPERATION: ");
    scanf("%d", &op);
    switch(op){
      case 1:
        insert(list);
        break;
      case 2:
        print(list);
        break;
      case 3:
        duplicate(list);
        break;
      case 5:
        printf("Closed!\n");
        break;
      default:
        printf("Invalid option!\n");
    }
  }while(op != 5);

  return 0;
}

Answer 1

在提出解决方案之前，我首先建议更改您的代码中的一些内容：

不要在专用函数中要求输入（如 insert）。在您的 main.
中执行此操作
在单独的函数中拆分一些逻辑：
- createNode 用于创建节点，
- getTail 用于查找对列表中最后一个节点的引用
然后使用这些使您的 insert 功能变得非常简单。然后，您还可以重用 createNode 在程序开始时创建“哨兵” list 节点，您也可以使用它来实现 duplicate.

这是建议的代码：

#include <stdio.h>
#include <stdlib.h>

typedef struct node{
  int x;
  struct node *next;
}Node;

// Check if the list is empty
int empty(Node *list){
  if(list->next == NULL)
    return 1;
  else
    return 0;
}

// Get a reference to the last node in the list, 
//   even if it is the sentinel node
Node *getTail(Node * list) {
  Node *tail = list;
  while (tail->next != NULL) {
    tail = tail->next;
  }
  return tail;
}

// Generic function for creating a Node instance
Node *createNode(int val, Node *next) {
  Node *newn = (Node *) malloc(sizeof(Node));
  newn->x = val;
  newn->next = next;
  return newn;
}

// Insert a number
void insert(Node *list, int val) {
  getTail(list)->next = createNode(val, NULL);
}

// Print the list (I changed the output format)
void print(Node *list) {
  list = list->next;
  while (list!=NULL) {
    printf("%d -> ", list->x);
    list = list->next;
  }
  printf("NULL\n");
}

// Duplicate X values in the list
void duplicate(Node *list, int val) {
  list = list->next;
  while (list != NULL) {
    if (list->x == val) {
      list->next = createNode(val, list->next);
      list = list->next; // reference the new node
    }
    list = list->next;
  }
}

int main(void) {
  Node *list = createNode(0, NULL); // Also use here!

  int op, val;

  do{
    printf("\n1 - Insert\n");
    printf("2 - Print\n");
    printf("3 - Duplicate X\n");
    printf("5 - Close\n");
    printf("OPERATION: ");
    scanf("%d", &op);
    switch(op){
      case 1:
        // Perform input in main program
        printf("\nNumber to insert: "); 
        scanf("%d", &val);
        insert(list, val);
        break;
      case 2:
        print(list);
        break;
      case 3:
        printf("\nNumber to duplicate: "); 
        scanf("%d", &val);
        duplicate(list, val);
        break;
      case 5:
        printf("Closed!\n");
        break;
      default:
        printf("Invalid option!\n");
    }
  } while(op != 5);

  return 0;
}

C 中的链表（中间插入）

Linked list in C (middle insert)

c

linked-list