数据结构——表的基本操作

创建一个单链表

#include <iostream>
#include<vector>

using namespace std;

struct ListNode{
	int val;
	struct ListNode* next;
	ListNode(int x) :
		val(x), next(NULL){
	}
};

int main(){
	int num;
	cin >> num;
	ListNode* head = new ListNode(num);
	ListNode* p = head;
	
	//利用尾插法创建一个链表
	while (cin >> num){
		ListNode* q = new ListNode(num);
		p->next = q; 
		p = p->next;
	}

	//遍历这个链表，并输出每个结点的元素
	ListNode* m = head;
	while (m != nullptr){
		cout << m->val << endl;
		m = m->next;
	}

	return 0;

}

插入结点

ListNode* insertNode(ListNode* head, int data){
	ListNode* newNode = new ListNode(data);
	ListNode* p = head;
	if (p == nullptr){
		head = newNode;
	}
	else{
		while (p->next != nullptr){
			p = p->next;
		}
		p->next = newNode;
	}
	return head;
}

删除结点

ListNode* deleteNode(ListNode* head, int data){
	ListNode* p = head;
	//首先判断是不是空链表
	if (p == nullptr){
		return head;
	}
	else{
		//判断是不是删除头节点
		if (p->val == data){
			head = p->next;
			delete p;
			return head;
		}
		else{
			//如果有该结点，遍历到待删除节点的前一节点
			while (p->next != nullptr && p->next->val != data){
				p = p->next;
			}
			//遍历完整个链表都没有待删除节点
			if (p->next == nullptr){
				return head;
			}
			else{
				ListNode* deleteNode = p->next;
				p->next = deleteNode->next;
				delete deleteNode;
				return head;
			}
		}
	}
}

反转链表

#include <iostream>
#include<vector>

using namespace std;

struct ListNode{
	int val;
	struct ListNode* next;
	ListNode(int x) :
		val(x), next(NULL){
	}
};

//反转链表
ListNode* reverse(ListNode* head){
	ListNode* pPrev = nullptr;
	ListNode* p = head;
	ListNode* pReverseHead = nullptr;
	while (p != nullptr){
		ListNode* pNext = p->next;
		if (pNext == nullptr){
			pReverseHead = p;
		}
		p->next = pPrev;
		pPrev = p;
		p = pNext;
	}
	return pReverseHead;
}

int main(){
	int num;
	cin >> num;
	ListNode* head = new ListNode(num);
	ListNode* p = head;
	while (cin >> num){
		ListNode* q = new ListNode(num);
		p->next = q;
		p = p->next;
	}
	p->next = nullptr;


	ListNode* result = reverse(head);
	ListNode* node = result;

	while (node != nullptr){
		cout << node->val << endl;
		node = node->next;
	}

	return 0;

}

倒数第k个结点

ListNode* FindKthToTail(ListNode* pListHead, unsigned int k) {
	if (pListHead == nullptr || k == 0){
		return nullptr;
	}

	ListNode* pAhead = pListHead;

	//判断K是不是超出了链表的长度
	for (int i = 0; i< k - 1; i++){
		if (pAhead->next != nullptr){
			pAhead = pAhead->next;
		}
		else{
			return nullptr;
		}
	}

	ListNode* pBehind = pListHead;
	while (pAhead->next != nullptr){
		pAhead = pAhead->next;
		pBehind = pBehind->next;
	}

	return pBehind;

}

判断是否有环

//判断快慢指针是否相遇
ListNode* MeetNode(ListNode* pHead){
    ListNode* pNode = pHead;
    //判断链表是否为空
    if(pNode == nullptr){
        return nullptr;
    }
    
    //设置慢指针（慢指针不能为nullptr）
    ListNode* slowNode = pNode -> next;
    if(slowNode == nullptr){
        return nullptr;
    }
    
	//设置快指针
    ListNode* fastNode = slowNode -> next;
    while(fastNode != nullptr && slowNode != nullptr){
    	//相遇返回快/慢指针
        if(fastNode == slowNode){
            return fastNode;
        }
        
        //slow走一步
        slowNode = slowNode ->next;
        //fast走两步（走下一步需要判读是不是为nullptr）
        fastNode = fastNode -> next;
        if (fastNode -> next != nullptr){
            fastNode = fastNode -> next;
        }
    }
    return nullptr;
}

//计算环中节点的个数
int Count(ListNode* pMeet){
    int count = 0;
    ListNode* pNode = pMeet;
    while(pNode->next != pMeet){
        ++count;
        pNode = pNode -> next;
    }
    ++ count;
    return count;
}

//计算环的入口节点
ListNode* EntryNodeOfLoop(ListNode* pHead)
{
    ListNode* meetNode = MeetNode(pHead);
    if (meetNode == nullptr){
        return nullptr;
    }
    
    int count = Count(meetNode);
    
    ListNode* aheadNode = pHead;
    ListNode* behindNode = pHead;
    
    for(int i = 0; i< count; i++){
        aheadNode = aheadNode ->next;
    }
   
    while(aheadNode != behindNode){
        aheadNode = aheadNode -> next;
        behindNode = behindNode -> next;
    }
    
    ListNode* result = aheadNode;
    return result;
}