c语言链表的删除节点这个代码有什么问题吗

Question

利用c语言里的链表删除大于k的节点，以0为结尾，输入k和链表，输出删除后的链表。（只会c语言，还没有学习c++）
不知道为什么代码运行错误，我是根据书上的链表删除的公式写的删除函数的，但是完全没发删除，感觉很苦恼
例子：
输入：2000
2001 2002 1999 1998 2021 1997 0
输出：1999 1998 1997

```c
#include<stdio.h>
#include<malloc.h>
struct cell
{
    int year;
    struct cell*next;
};
struct cell*build(void)
{
    struct cell*head,*p,*tmp;
    int n;
    head=p=tmp=NULL;
    scanf("%d",&n);
    if(n==0)
    {
        return head;
    }
    p=(struct cell*)malloc(sizeof(struct cell));
    p->year=n;
    p->next =NULL;
    head=p;
    scanf("%d",&n);
    while(n!=0)
    {
        tmp=(struct cell*)malloc(sizeof(struct cell));
        tmp->year=n;
        tmp->next=NULL;
        p->next=tmp;
        p=p->next;
        scanf("%d",&n);
    }
    return head;
};
struct cell*delect(struct cell*head,int k)
{
    struct cell*p,*p0,*p1;
    p=head;
    p0=NULL;
    if(head==NULL){return head;}
    while(p->year>k)
    {p=p->next;free(p0->next);p0->next=p;

    }

   head=p;

    while(p!=NULL)
    {
        if(p->year>k){p=p->next;free(p0->next);p0->next=p;}
        p0=p;p=p->next;

    }
    return head;
};
void print(struct cell*head)
{
    struct cell*p;
    p=head;
    if(head==NULL){printf("NULL");return;}
    while(p!=NULL)
    {
        printf("%d",p->year);
        if(p->next!=NULL){printf(" ");}
    }
}
void release(struct cell*head)
{
    struct cell*p0,*p;
    p=head;
    while(p!=NULL)
    {
        p0=p;p=p->next;free(p0);
    }
}
int main()
{
    struct cell*head;int k;
    scanf("%d",&k);
    head=build();

    head=delect(head,k);
    print(head);
    release(head);
    return 0;
}

Answer 1

您的代码中存在一些问题：

在 delect() 函数中，当链表头的值大于 k 时，您直接让 head 指向当前节点 p，但是却没有释放原来的头节点空间，导致内存泄漏。可以先将当前节点 p 存到 p1 中，再释放 p0。

在 print() 函数中，每输出一个节点的值后都应该将 p 指向下一个节点，否则会造成死循环输出。

在输出节点的值时，应该加上换行符，否则多个值会输出在同一行，不易阅读。

下面是修改后的代码，您可以参考一下：

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

struct cell {
    int year;
    struct cell *next;
};

struct cell *build(void) {
    struct cell *head, *p, *tmp;
    int n;
    head = p = tmp = NULL;
    scanf("%d", &n);
    if (n == 0) {
        return head;
    }
    p = (struct cell*)malloc(sizeof(struct cell));
    p->year = n;
    p->next = NULL;
    head = p;
    scanf("%d", &n);
    while (n != 0) {
        tmp = (struct cell*)malloc(sizeof(struct cell));
        tmp->year = n;
        tmp->next = NULL;
        p->next = tmp;
        p = p->next;
        scanf("%d", &n);
    }
    return head;
}

struct cell *delect(struct cell *head, int k) {
    struct cell *p, *p0, *p1;
    p = head;
    p0 = NULL;
    if (head == NULL) {
        return head;
    }
    while (p->year > k) {
        p1 = p;
        p = p->next;
        free(p1);
    }

    head = p;

    while (p != NULL) {
        if (p->year > k) {
            p1 = p;
            p = p->next;
            free(p1);
            p0->next = p;
        } else {
            p0 = p;
            p = p->next;
        }
    }
    return head;
}

void print(struct cell *head) {
    struct cell *p;
    p = head;
    if (head == NULL) {
        printf("NULL\n");
        return;
    }
    while (p != NULL) {
        printf("%d\n", p->year);
        p = p->next;
    }
}

void release(struct cell *head) {
    struct cell *p0, *p;
    p = head;
    while (p != NULL) {
        p0 = p;
        p = p->next;
        free(p0);
    }
}

int main() {
    struct cell *head;
    int k;
    scanf("%d", &k);
    head = build();

    head = delect(head, k);
    print(head);
    release(head);
    return 0;
}