算法复习：链表

Posted 2021-03-09 dzzy

链表必须清楚掌握

链表定义

struct ListNode 
{
    int val;
    ListNode *next;
};

创建链表头

ListNode* creat()//创建头
{
    struct ListNode *node=(struct ListNode *)malloc(sizeof(struct ListNode));
    node->next=NULL;
    return node;
}

创建一个新节点（插入时调用）

ListNode* make_node(int num)//建新节点
{
    struct ListNode *node=(struct ListNode *)malloc(sizeof(struct ListNode));
    node->val=num;
    node->next=NULL;
    return node;
}

插入新节点（尾插法）

ListNode* insert(ListNode* head,int num)//尾插法
{
    struct ListNode *str=(struct ListNode *)malloc(sizeof(struct ListNode));
    str=head;
    while(str->next)
    {
        str=str->next;
    }
    str->next=make_node(num);
    return head;
}

插入新节点（头插法）

ListNode* insert(ListNode* head,int num)//头插法
{
    struct ListNode *str=make_node(num);
    str->next=head->next;
    head->next=str;
    return head;
}

主函数举例（遍历输出，头节点不存数据）

int main()
{
    struct ListNode *head=creat();
    insert(head,1);
    insert(head,1);
    insert(head,2);
    insert(head,3);
    insert(head,4);
    insert(head,4);
    insert(head,5);
    struct ListNode *str=head->next;
    while(str)
    {
        cout<<str->val<<" ";
        str=str->next;
    }
    cout<<endl;
    return 0;
}

使用举例

leedcode 82. 删除排序链表中的重复元素 II

/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode(int x) : val(x), next(NULL) {}
 * };
 */
class Solution {
public:
    ListNode* deleteDuplicates(ListNode* head)
    {
        struct ListNode* pass;
        struct ListNode* slow;
        struct ListNode* fast;
        if(head==NULL||head->next==NULL)
            return head;
        
        //处理头节点要删除的情况 递归删除
        int lables=0;
        while(head!=NULL&&head->next!=NULL&&head->val==head->next->val)
        {
            struct ListNode* tmp;
            tmp=head->next;
            head->next=tmp->next;
            delete tmp;
            lables=1;
        }
        if(lables==1)
        {
            head=head->next;
            head=deleteDuplicates(head);
        }
        if(head==NULL)
            return head;
        pass=head;
        if(pass==NULL||pass->next==NULL||pass->next->next==NULL)
            return head;
        slow=pass->next;
        fast=slow->next;
        if(slow->val==fast->val&&fast->next==NULL)
        {
            delete slow;
            delete fast;
            head->next=NULL;
            return head;
        }
        int lable=0;
        while(1)
        {
            if(fast==NULL&&lable==0)
                return head;
            if(fast==NULL&&lable==1)
            {
                pass->next=NULL;
                return head;
            }    
            if(slow->val!=fast->val&&lable==0)//相邻不等
            {
                pass=slow;
                slow=fast;
                fast=fast->next;
                lable=0;
                continue;
            }
            if(slow->val==fast->val)//slow=fast
            {
                struct ListNode* tmp;
                tmp=fast;
                fast=fast->next;
                delete tmp;
                lable=1;
                continue;
            }
            if(slow->val!=fast->val&&lable==1)//不相邻不相等
            {
                pass->next=fast;
                slow=fast;
                fast=fast->next;
                lable=0;
                continue;
            }
        }
        return head;
    }
};

leedcode 82