在链表中插入节点的函数

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

// 定义链表的节点结构
struct ListNode {
    int val;
    struct ListNode *next;
};

// 在链表中插入节点的函数
void insertNode(struct ListNode **head, int value, int position) {
    // 创建新节点
    struct ListNode *newNode = (struct ListNode *) malloc(sizeof(struct ListNode));
    newNode->val = value;

    // 若插入位置为链表头部
    if (position == 0) {
        newNode->next = *head;
        *head = newNode;
    }
    // 若插入位置不是链表头部
    else {
        struct ListNode *currentNode = *head;
        int count = 0;
        
        // 遍历找到插入位置的前一个节点
        while (currentNode != NULL && count < position - 1) {
            currentNode = currentNode->next;
            count++;
        }
        
        // 插入新节点
        newNode->next = currentNode->next;
        currentNode->next = newNode;
    }
}

// 测试
int main() {
    // 创建链表：1 -> 2 -> 4
    struct ListNode *head = (struct ListNode *) malloc(sizeof(struct ListNode));
    struct ListNode *node2 = (struct ListNode *) malloc(sizeof(struct ListNode));
    struct ListNode *node4 = (struct ListNode *) malloc(sizeof(struct ListNode));
    head->val = 1;
    head->next = node2;
    node2->val = 2;
    node2->next = node4;
    node4->val = 4;
    node4->next = NULL;

    // 在链表中插入新节点：3
    insertNode(&head, 3, 2);

    // 输出链表：1 -> 2 -> 3 -> 4
    struct ListNode *currentNode = head;
    while (currentNode != NULL) {
        printf("%d ", currentNode->val);
        currentNode = currentNode->next;
    }
    printf("\n");

    // 释放链表内存
    while (head != NULL) {
        struct ListNode *temp = head;
        head = head->next;
        free(temp);
    }
    
    return 0;
}