关于链表

//
// Created by Administrator on 2021/8/1.
//

#ifndef C__TEST01_LINKNODE_HPP
#define C__TEST01_LINKNODE_HPP

#include <map>
#include <unordered_map>
#include <unordered_set>

class LinkNode{
public:
    int value;
    LinkNode *next;
    LinkNode(int value):value(value){}
};
/*
 * circle = true, LinkList has a circle
 * circle = false, LinkList doesn't have a circle
 * */
LinkNode* linkInitDouble(bool circle = false){
    LinkNode *head = new LinkNode(3);
    head->next = NULL;
    if(circle){
        LinkNode *L = new LinkNode(rand()%10);
        head->next = L;
        L->next = NULL;
        LinkNode *p = L;
        for (int i = 0; i < 6; ++i) {
            L = new LinkNode(rand()%10);
            L->next = NULL;
            p->next = L;
            p = L;
        }
        p = head;
        for(int i = 0; i<3 + rand()%3; ++i){
            p = p->next;
        }
        L->next = p;
    }else{
        LinkNode *L = new LinkNode(rand()%10);
        head->next = L;
        L->next = NULL;
        LinkNode *p = L;
        for (int i = 0; i < 6; ++i) {
            L = new LinkNode(rand()%10);
            L->next = NULL;
            p->next = L;
            p = L;
        }
    }
    return head;
}

/*
 * circle = true, LinkList has a circle
 * circle = false, LinkList doesn't have a circle
 * */
LinkNode* linkInitSingle(bool circle = false){
    LinkNode *head = new LinkNode(3);
    head->next = NULL;
    if(circle){
        LinkNode *L = new LinkNode(rand()%10);
        head->next = L;
        L->next = NULL;
        LinkNode *p = L;
        for (int i = 0; i < 7; ++i) {
            L = new LinkNode(rand()%10);
            L->next = NULL;
            p->next = L;
            p = L;
        }
        p = head;
        for(int i = 0; i<3 + rand()%3; ++i){
            p = p->next;
        }
        L->next = p;
    }else{
        LinkNode *L = new LinkNode(rand()%10);
        head->next = L;
        L->next = NULL;
        LinkNode *p = L;
        for (int i = 0; i < 7; ++i) {
            L = new LinkNode(rand()%10);
            L->next = NULL;
            p->next = L;
            p = L;
        }
    }
    return head;
}

LinkNode *getMidLink(LinkNode *L){
    LinkNode *slow = L;
    LinkNode *fast = L->next;//get mid+1
    //LinkNode *fast = L->next; get mid
    while (fast->next != NULL){
        slow = slow->next;
        fast = fast->next->next;
        if(fast == NULL){
            return slow;
        }
    }
    return slow;
}
bool isCircle(LinkNode *L){
    LinkNode *slow = L;
    LinkNode *fast = L->next->next;
    while(slow != fast){
        slow = slow->next;
        fast = fast->next->next;
        if(fast == NULL || fast->next == NULL){
            return false;
        }
    }
    return true;
}
LinkNode *getEnterCirclePointer(LinkNode *L){
    LinkNode *slow = L->next;
    LinkNode *fast = L->next->next;
    while(slow != fast){
        if(fast == NULL || fast->next == NULL){
            return NULL;
        }
        slow = slow->next;
        fast = fast->next->next;
    }
    fast = L;
    while(slow != fast){
        slow = slow->next;
        fast = fast->next;
    }
    return slow;
}

LinkNode *getEnterCirclePointerByHash(LinkNode *L){
    unordered_set<LinkNode*> hashSet;
    while(L != NULL){
        hashSet.insert(L);
        L = L->next;
        if(hashSet.find(L) != hashSet.end()){
            return L;
        }
    }
    return L;
}

/*题目：
 * 对于一个链表，分成小于一个阈值，等于一个阈值，大于一个阈值三个部分
 * 三个阈值都一样
 * */
LinkNode* dutchFlagByLinkList(LinkNode *L, int value){
    LinkNode *minStart = NULL;
    LinkNode *minEnd = NULL;
    LinkNode *equalStart = NULL;
    LinkNode *equalEnd = NULL;
    LinkNode *maxStart = NULL;
    LinkNode *maxEnd = NULL;
    LinkNode *start = NULL;
    while(L != NULL){
        if(L->value < value){
            if(minStart == NULL){
                minStart = L;
                minEnd = L;
            }else{
                minEnd->next = L;
                minEnd = L;
            }
        }else if(L->value == value){
            if(equalStart == NULL){
                equalStart = L;
                equalEnd = L;
            }else{
                equalEnd->next = L;
                equalEnd = L;
            }
        }else{
            if(maxStart == NULL){
                maxStart = L;
                maxEnd = L;
            }else{
                maxEnd->next = L;
                maxEnd = L;
            }
        }
        L = L->next;
    }
   if(minStart != NULL){
       minEnd->next = equalStart;
       equalEnd = equalEnd != NULL? equalEnd:minEnd;
   }

   if(equalEnd != NULL){
       equalEnd->next = maxStart;
   }
   return minStart != NULL? minStart:(equalStart!=NULL?equalStart:maxStart);
}
#endif //C__TEST01_LINKNODE_HPP