循环链表

时间：2013-12-12 09:55:18

标签： c circular-list

我的圆形链表代码适用于添加，搜索，计数，查看但是一旦我删除列表中的条目，它就会与列表中的所有其他数据混淆。 我知道错误在 DeleteNode 函数中，但无法解决。 请帮帮我 - 谢谢。

#include <stdio.h>
#include <conio.h>
#include <stdlib.h>
struct Node{
    int data;
    struct Node *next;
}*head,*temp,*curr,*prev,*p;
/*   Prototypes   */
void AddNode(int value);
int CountNode();
void SearchNode(int value);
void ViewAll();
void DeleteNode(int value);
/* Main */
int main(){
    int choice,value;
    printf("\n\n\n\t\t\tCircular Linked List\n\n\t\t\tSyed Danish Ali\n\n\t\t\tUBIT\n\n\n\t\t\t\tHit ENTER to continue...");
    while(getche() != '\r'){
    }
    do{
        system("cls");
        printf("\n\nMENU\n=====\n\n[1] ADD\n[2] COUNT\n[3] SEARCH\n[4] VIEW ALL [5] DELETE\n[6] EXIT\n\nCHOICE:\t");
        scanf("%d",&choice);
        if(choice == 1){
        printf("Enter data:\t"); scanf("%d",&value);
        AddNode(value);
        getch();
        } else if(choice == 2){
        printf("\n\n%d Node(s).",CountNode());
        getch();
        }else if(choice == 3){
        printf("Enter the data to search:\t");
        scanf("%d",&value);
        SearchNode(value);
        getch();
        } else if(choice == 4){
        ViewAll();
        getch();
        } else if(choice == 5){
        printf("Enter the data to search:\t");
        scanf("%d",&value);
        DeleteNode(value);
        getch();
        } else if(choice == 6){
            return 0;
        }

    }while(1);
}

void AddNode(int value){
    temp = (struct Node *) malloc (sizeof(struct Node));
    temp->data = value;

    if(head == NULL){
    head = temp;
    temp->next = head;
    } else {
    curr = head;
    while(curr->next != head){
        curr = curr->next;
    }
    p = curr;
    curr->next = temp;
    temp->next = head;
    }
    printf("\n\nNode added.");
}
int CountNode(){
    int k = 0;
    if(head == NULL){
    return 0;
    } else {
    curr = head;
    while(curr->next != head){
        k++;
        curr = curr->next;
    }
    return k;
    }
}
void SearchNode(int value){
    int flag = 0,k = 0;
    if (head == NULL){
    printf("\n\nList is empty.");
    } else {
    curr = head;
    while(curr->next != head){
        if (curr->data == value){
        flag = 1;
        printf("\n\n%d found at index # %d.",value,k);
        curr = curr->next;
        } else {
        curr = curr->next;
        k++;
        }
    }
    }
    if(flag == 0)
    printf("\n\nValue %d not found.",value);
}
void ViewAll(){
    int counter = 0;
    if(head == NULL)
    printf("\n\nList is empty.");
    else{
    curr = head;
    printf("LIST GENERATED:\n===============\n");
    while(curr->next != head){
        printf("\nElement # %d:\nData:\t%d",counter+1,curr->data);
        curr = curr->next;
        counter++;
    }
    }
}
void DeleteNode(int value){
    int flag = 0;
    if(head == NULL){
    printf("\n\nList is empty.");
    } else {
    curr = head;
    while(curr->next != head){
        if(curr->data == value){
        printf("\n\nValue found.");
        flag = 1;
        if(curr == head){
            curr->next = head;
            free(curr);

        } else {
            prev->next = curr->next;
            free(curr);
        }
        } else {
        prev = curr;
        curr = curr->next;
        }
    }
    printf("Node deleted.");
    }
    if(flag == 0)
    printf("\n\nValue not found.");
}

4 个答案:

答案 0 :(得分：2)

} else {
        prev->next = curr->next;  //here prev doesn't point to any memory address so
                                    we can't assign value to prev->next
        free(curr);
    }

答案 1 :(得分：0)

你有一个圆形清单。这意味着无论何时删除节点，无论是否为头，都会有前一个节点。

此代码可以缩短，也可以解决您的问题。

    if(curr == head){
        curr->next = head;
        free(curr);

    } else {
        prev->next = curr->next;
        free(curr);
    }

要

    prev->next = curr->next;
    if(curr == head)
         head = curr->next;
    free(curr);

您的原始代码设置了curr-＆gt;紧靠头部而不是相反，从而最终进入curr-＆gt;接下来指向curr（等于head）。

编辑：

但是，您还应该检查curr-＆gt; next是否等于它本身，这意味着您要删除循环链接列表中的最后一个节点。

答案 2 :(得分：0)

你的代码很好，我完全看了它并发现了错误。 你只需要在释放节点后添加break。而已。 :) 在释放节点后，它再次移动并且当前为空..所以它会中断。

void DeleteNode(int value){
    int flag = 0;
    if(head == NULL){
    printf("\n\nList is empty.");
    } else {
    curr = head;
    while(curr->next != head){
        if(curr->data == value){
        printf("\n\nValue found.");
        flag = 1;
        if(curr == head){
            curr->next = head;
            free(curr);
            break;  // this is where it break

        } else {
            prev->next = curr->next;
            free(curr);
            break;  // this is where it break
        }
        } else {
        prev = curr;
        curr = curr->next;
        }
    }
    printf("Node deleted.");
    }
    if(flag == 0)
    printf("\n\nValue not found.");
}

要继续ittrating并删除具有相同值的所有节点，您可以在else语句中使用它。

else {
            prev->next = curr->next;
            free(curr);
            curr=prev; // this what you need
            break;  
        }

答案 3 :(得分：0)

很好的实施。 我发现了以下错误：

  1. 遍历列表时，忽略了头部。下面，while-loops已被替换为搜索，查看和删除功能的do-while。

  2. 如前所述，删除功能中未为prev分配有效值。

  3. 删除头部时，prev-＆gt; next未更改。在这种情况下，无论如何都没有设置prev。在下面的代码中，添加了一个尾部变量。这样，prev可以在删除功能的开头设置。否则，列表也已经确定，像curr和prev这样的全局变量总是有一个有效的值。

    4. 我希望这可能有用。 干杯， 迈克尔

    修改后的代码：

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

struct Node
{
  int data;
  struct Node *next;
}*head,*temp,*curr,*prev,*tail;

/*   Prototypes   */
void AddNode(int value);
int  CountNode();
void SearchNode(int value);
void ViewAll();
void DeleteNode(int value);

/* Main */
int main()
{
  int choice,value;
  printf("\n\n\n\t\t\tCircular Linked List\n\n\t\t\tSyed Danish Ali\n\n\t\t\tUBIT\n\n\n\t\t\t\tHit ENTER to continue...");
  while(getche() != '\r')
  {
  }
  do
  {
    system("cls");
    printf("\n\nMENU\n=====\n\n[1] ADD\n[2] COUNT\n[3] SEARCH\n[4] VIEW ALL\n[5] DELETE\n[6] EXIT\n\nCHOICE:\t");
    scanf("%d",&choice);
    if(choice == 1){
      printf("Enter data:\t"); scanf("%d",&value);
      AddNode(value);
      getch();
    } else if(choice == 2){
      printf("\n\n%d Node(s).",CountNode());
      getch();
    }else if(choice == 3){
      printf("Enter the data to search:\t");
      scanf("%d",&value);
      SearchNode(value);
      getch();
    } else if(choice == 4){
      ViewAll();
      getch();
    } else if(choice == 5){
      printf("Enter the data to search:\t");
      scanf("%d",&value);
      DeleteNode(value);
      getch();
    } else if(choice == 6){
      return 0;
    }
  } while(1);
}

void AddNode(int value)
{
  temp = (struct Node *) malloc (sizeof(struct Node));
  temp->data = value;

  if(head == NULL)
  {
    head = temp;
    tail = temp;
    curr = temp;
    temp->next = head;
  } else {
    // remember prev if needed
    prev       = tail;
    prev->next = temp;
    tail       = temp;
    curr       = temp;
    temp->next = head;
  }
  // remember tail
  printf("\n\nNode added.");
  }
  int CountNode(){
  int k = 0;
  if(head == NULL){
    return 0;
  } else {
    temp = head;
    // count head, too
    do
    {
      k++;
      temp = temp->next;
    } while(temp != head);
    return k;
  }
}

void SearchNode(int value){
  int flag = 0,k = 0;
  if (head == NULL){
     printf("\n\nList is empty.");
  } else {
    curr = head;
    // search head, too
    do
    {
      if (curr->data == value){
        flag = 1;
        printf("\n\n%d found at index # %d.",value,k);
        curr = curr->next;
      } else {
        curr = curr->next;
        k++;
      }
    } while(curr != head);
  }
  if(flag == 0)
  {
    printf("\n\nValue %d not found.",value);
  }
}

void ViewAll(){
  int counter = 0;
  if(head == NULL)
  {
    printf("\n\nList is empty.");
  } else {
    curr = head;
    printf("LIST GENERATED:\n===============\n");
    // show head, too
    do
    {
      printf("\nElement # %d:\nData:\t%d",counter+1,curr->data);
      curr = curr->next;
      counter++;
    } while(curr != head);
  }
}

void DeleteNode(int value){
  int flag = 0;
  if(head == NULL)
  {
    printf("\n\nList is empty.");
  } else {
    curr = head;
    prev = tail;
    // delete head, too, if it contains the searched value
    do{
      if(curr->data == value)
      {
        printf("\n\nValue found.");
        flag = 1;
        if(curr == head)
        {
          if(tail == head)
          {
            // list contains only one element
            free(head);
            temp = NULL;
            head = NULL;
            prev = NULL;
            curr = NULL;
            tail = NULL;
          } else {
            // list contains more than one element
            temp = curr;
            free(temp);
            temp = tail; // ensure, temp is valid
            curr = head->next;
            head = curr;
            tail->next = curr;
            // prev = tail;
          }

        } else {
          // curr != head
          prev->next = curr->next;
          if(curr == tail){
            tail = prev; // tail may be head as well, now
          } else {
            // nothing to do ;O)
          }
          free(curr);
          curr = prev->next;
          temp = prev; // ensure, temp is valid
        }
      } else {
        // don't delete, just advance
        prev = curr;
        curr = curr->next;
      }
    } while(curr != head);
    printf("Node deleted.");
  }
  if(flag == 0)
  {
    printf("\n\nValue not found.");
  }
}
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