【链表】2、带头结点链表删除指定值

/*
    在带头结点的单链表L中,删除所有值为X的节点，并释放其空间，假设值为X的节点不唯一
    分析：
        和上题相似，只是多了一个头结点。
*/
struct Link {
    int data;
    struct Link *next;
};
#define _CRT_SECURE_NO_WARNINGS
#include <stdio.h>
#include <stdlib.h>
void deleteX(Link *p,int delNum) {
    /*struct Link* q;//这是递归方法
    if (p == NULL) return;
    if (p->data==delNum) {
        q = p;
        p = p->next;
        free(q);
        deleteX(p,delNum);
    }
    else {
        deleteX(p->next, delNum);
    }*/
    //不采取递归，直接遍历
    struct Link *pre = p, *q = p->next,*r;
    while (q) {
        if (q->data==delNum) {
            r = q;//r指向待删除节点
            q = q->next;//
            pre->next = q;//删除节点
            free(r);//释放节点
        }
        else {
            pre = q;
            q = q->next;
        }
    }
}
int main() {
    //创建节点
    struct Link *head = (struct Link*)malloc(sizeof(struct Link));
    struct Link *q = (struct Link*)malloc(sizeof(struct Link));
    q = head;
    head->next = NULL;
    int n,data,delNum;
    printf("请输入节点个数：");
    scanf("%d",&n);
    for (int i = 0; i < n;i++) {
        printf("请输入第%d个节点值：",i+1);
        struct Link *p = (struct Link*)malloc(sizeof(struct Link));
        scanf("%d",&data);
        p->data = data;
        head->next = p;
        head = p;
    }
    head->next = NULL;//这里要将指针的next指向NULL，不然后面的判断会出问题，而且这也是应该养成的好习惯
    head = q;//head回到头结点
    printf("当前链表值为：");
    while (head->next) {
        printf("%d ",head->next->data);
        head = head->next;
    }
    printf("\n");
    printf("请输入要删除的值：");
    scanf("%d",&delNum);
    head = q;//head回到头结点
    deleteX(head,delNum);
    printf("删除后链表值为：");
    while (head->next) {
        printf("%d ", head->next->data);
        head = head->next;
    }
    return 0;
}