手撕链表（自存）

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

typedef int E;

typedef struct node {
    E val;
    struct node* next;
}ListNode;

ListNode* list_creat() {
    ListNode* list = malloc(sizeof(ListNode));
    return list;
}

void push_back(ListNode* List, E val) {
    if (!List)
    {
        printf("List is NULL!");
        exit(1);
    }
    ListNode* p = malloc(sizeof(ListNode));
    if (!p) {
        printf("error");
        exit(1);
    }
    p->val = val;
    p->next = NULL;//尾插法，新元素next为空
    ListNode* tail = List;
    while (tail->next) {
        tail = tail->next;
    }
    tail->next = p;
}

void push_front(ListNode** List, E val) {
    ListNode* p = malloc(sizeof(ListNode));
    if (!p) {
        printf("error");
        exit(1);
    }
    p->val = val;
    p->next = *List;
    *List = p;
}

E pop_back(ListNode *List) {
    if (List == NULL)
    {
        printf("error");
        exit(1);
    }
    ListNode* pre, * curr;
    pre = NULL;
    curr = List;
    while (curr) {
        pre = curr;
        curr = curr->next;
    }
    E value = curr->val;
    free(curr);
    pre->next = NULL;
    return value;
}

E pop_front(ListNode** List) {
    E value = (*List)->val;
    ListNode* p = malloc(sizeof(ListNode));
    p = *List;
    *List = p->next;
    free(p);
    return value;
}

void destroy_list(ListNode* List) {
    ListNode* curr, * next;
    curr = List;
    while (curr) {
        next = curr->next;
        free(curr);
        curr = next;
    }
    free(List);
}

int main(void) {
ListNode* list = list_creat();
push_back(list, 1);
push_back(list, 4);
push_back(list, 8);
push_back(list, 9);
add_before_head(&list, 10);
return 0;
}