1.2 链表

链表，别名链式存储结构或单链表，用于存储逻辑关系为 "一对一" 的数据。与顺序表不同，链表不限制数据的物理存储状态，换句话说，使用链表存储的数据元素，其物理存储位置是随机的。

链表的创建及增删改查

#include "stdafx.h"

typedef struct Link {
    char elem;
    struct Link * next; 
}link;

link * initLink() {
    //link * p = NULL; //头指针
    //link * temp = (link*)malloc(sizeof(link)); //临时节点
    link * p = (link*)malloc(sizeof(link));// 头节点用于遍历
    link *temp = p;

    for (int i = 1; i < 5; i++) {
        link * a = (link*)malloc(sizeof(link));
        a->elem = i*2;
        a->next = NULL;
        temp->next = a; //临时节点（前驱）指向 a（后继），存储 a 的位置
        temp = temp->next; //临时节点向后移一位
    }
    return p;
}

void display(link *p) {
    link *temp = p->next;
    while (temp) {
        printf("%d ", temp->elem);
        temp = temp->next;
    }
    printf("\n");
}

link * insertElem(link * p, int elem, int add) {
    link * temp = p;
    for (int i = 1; i < add; i++) {
        if (temp == NULL) {
            printf("Invalid address for inserting\n");
            return p;
        }
        temp = temp->next;
    }
    link *c = (link*)malloc(sizeof(link));
    c->elem = elem;
    c->next = temp->next;
    temp->next = c;
    return p;
    
}

link * delElem(link* p, int add) {
    link *temp = p;
    for (int i = 1; i < add; i++) {
        if (temp == NULL) {
            printf("Invalid address for deleting\n");
            return p;
        }
        temp = temp->next;
    }
    link * del = temp->next;
    temp->next = temp->next->next;
    free(del);//释放内存
    return p;
}

link * updateElem(link *p, int add, int newElem) {
    link * temp = p->next;
    for (int i = 1; i < add; i++) {
        if (temp == NULL) {
            printf("Invalid address for updating\n");
            return p;
        }
        temp = temp->next;
    }
    temp->elem = newElem;
    return p;
}

int selectElem(link * p, int elem) {
    link * temp = p->next;
    int i = 1;
    while (temp) {
        if (temp->elem == elem)
            return i;
        temp = temp->next;
        i++;
    }
    return -1;
}

int main() {
    printf("初始化链表为：\n");
    link *p = initLink();
    display(p);

    printf("在位置3前插入元素5\n");
    insertElem(p, 5, 3);
    display(p);

    printf("删除位置3的元素\n");
    delElem(p, 3);
    display(p);

    printf("查找元素6所在位置\n");
    printf("%d \n", selectElem(p, 6));
    
    printf("将位置3的元素改为10\n");
    updateElem(p, 3, 10);
    display(p);

    return 0;
}