剑指Offer11 在O(1)内删除链表结点

/*************************************************************************
    > File Name: 11_DeleteLinkNode.c
    > Author: Juntaran
    > Mail: JuntaranMail@gmail.com
    > Created Time: 2016年08月30日 星期二 02时10分27秒
 ************************************************************************/

#include <stdio.h>
#include <malloc.h>
#include <string.h>

// 链表结构体
struct ListNode
{
    int val;
    ListNode* next;
};

// 构造链表
ListNode* createList()
{
    struct ListNode* head;
    struct ListNode* p;
    struct ListNode* q;
    head = p = (ListNode*)malloc(sizeof(ListNode));
    head->val = 0;
    for (int i = 1; i <= 10; ++i)
    {
        q = (ListNode*)malloc(sizeof(ListNode));
        q->val = i;
        p->next = q;
        p = q;
    }
    p->next = NULL;
    return head;
}

// 顺序输出链表
void PrintList(ListNode* head)
{
    if (head == NULL)
        return;
    ListNode* temp = head;
    printf("PrintList:
");
    while (temp != NULL)
    {
        printf("%d ", temp->val);
        temp = temp->next;
    }
    printf("
");
}

// 删除结点
void DeleteListNode(ListNode** head, ListNode* key)
{
    if (head==NULL || key==NULL)
        return;
    
    // 如果要删除头结点
    if (*head == key)
    {
        *head = (*head)->next;
        free(key);
        key = NULL;
        return;
    }
    
    // 如果要删除尾结点
    if (key->next == NULL)
    {
        ListNode* temp = *head;
        while (temp->next != key)
            temp = temp->next;
        
        temp->next = NULL;
        free(key);
        key = NULL;
        return;
    }
    
    // 其他情况
    ListNode* temp = key->next;
    key->val = temp->val;
    key->next = temp->next;
    
    free(temp);
    temp = NULL;
    
}


int main()
{
    ListNode* test = createList();
    PrintList(test);
    
    ListNode* key1 = test;                // 头结点测试
    ListNode* key2 = test->next->next;    // 正常情况测试
    ListNode* key3 = test;
    while (key3->next)
    {
        key3 = key3->next;                // 尾结点测试
    }
    
    printf("key1 is %d
", key1->val);
    printf("key2 is %d
", key2->val);
    printf("key3 is %d
", key3->val);
    
    DeleteListNode(&test, key1);
    PrintList(test);
    DeleteListNode(&test, key2);
    PrintList(test);
    DeleteListNode(&test, key3);
    PrintList(test);
    
    return 0;
}