C语言实现链表的生成、删除、插入

C语言实现链表的生成、删除、插入

讲解视频

讲解视频

/*
 * Author:  Mingchong Li
 * Email:   19726006@bjtu.edu.cn
 * Date:    2022/1/8
 */

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


/* Define the node
 * If we don't use `typedef` here,
 * we have to call it `struct nodes` instead of `node`.
*/
typedef struct nodes {
    int num;                     // store data
    struct nodes *next;          // point to the next node
} node;                          // here we can define other names of node

/*
 * Create the a link list for the given array.
 * int x[]: given an integer array
 * int n:   preset the size of array
 */
node *create(int x[], int n) {
    // the head will return at last
    node *head = (node *) malloc(sizeof(node));
    if (n == 0) {
        return NULL;                                    // if here is an empty array
    }
    head->num = x[0];                                   // the first num
    head->next = NULL;                                  // if the array is size of 1, the head will be the tail
    node *p = head;                                     // p is an "allocator", allocate nums from the next of head
    for (int i = 1; i < n; i++) {
        p->next = (node *) malloc(sizeof(node));    // store in heap
        p->next->num = x[i];                             // store the num
        p = p->next;                                     // go to the next
        p->next = NULL;                                  // if it is the end, then next is NULL
    }
    return head;
}

/*
 * display all of the node's num
 */
void display(const node *head) {
    const node *p = head;
    for (; p != NULL; p = p->next) {
        printf("%d ", p->num);      // print until NULL
    }
    printf("\n");
}

/*
 * insert x to the head on n
 * n < 0 or n >= size of link list will return
 */
void insert(node *head, int x, int n) {
    node *p = head;

    if (n == 0) {
        // the head will be copied and insert to the next of head
        insert(head, head->num, 1);
        // change the num of head to x
        head->num = x;
        return;
    } else if (n < 0)
        return;

    // locate to the pre one of n
    for (int i = 0; i < n - 1; i++) {
        p = p->next;
        if (p == NULL)
            return;
    }
    node *preNext = p->next;
    p->next = (node *) malloc(sizeof(node));
    p->next->num = x;
    p->next->next = preNext;
}

/*
 * delete the node position on n
 */
void delete(node *head, int n) {
    node *p = head;

    // we can't delete the head, for the pointer to head couldn't be changed
    // so we just copy the next one to head, and delete the next one
    if (n == 0) {
        p->num = p->next->num;
        delete(head, 1);
    }

    for (int i = 0; i < n - 1; i++) {
        p = p->next;
        if (p == NULL)
            return;
    }

    p->next = p->next->next;            // delete
}

int main() {
    int arr[] = {1, 3, 5, 7, 9};

    node *linkList = create(arr, sizeof(arr) / sizeof(int));
    display(linkList);

    insert(linkList, 0, 0);
    display(linkList);

    delete(linkList, 0);
    display(linkList);

    free(linkList);             // free heap
    return 0;
}