LeetCode Q206: Reverse Linked List

Reverse a singly linked list.

	/**
	* Definition for singly-linked list.
	* struct ListNode {
	* int val;
	* ListNode *next;
	* ListNode(int x) : val(x), next(NULL) {}
	* };
	*/
	class Solution {
	public:
	void helper(ListNode* head, int l){
	if(l==0)
	return;
	ListNode* p=head;
	int c=l;
	while(c-- > 1){p=p->next;}
	p->next->next=p;
	p->next=NULL;
	helper(head, l-1);
	}
	ListNode* reverseList(ListNode* head) {
	if(head==NULL)
	return head;
	int l=0;
	ListNode* newHead=head;
	while(newHead->next!=NULL){
	newHead=newHead->next;
	l++;
	}
	helper(head, l);
	return newHead;
	}
	};

view raw Q206ReverseLinkedList.cpp hosted with ❤ by GitHub

	/**
	* Definition for singly-linked list.
	* struct ListNode {
	* int val;
	* ListNode *next;
	* ListNode(int x) : val(x), next(NULL) {}
	* };
	*/
	class Solution {
	public:
	ListNode* reverseList(ListNode* head) {
	if(head==NULL)
	return head;
	ListNode* pre=head;
	ListNode* cur = head->next;
	pre->next = NULL;
	ListNode* next;
	while(cur!=NULL){
	next = cur->next;
	cur->next = pre;
	pre = cur;
	cur = next;
	}
	return pre;
	}
	};

view raw Q206Rnd2.cpp hosted with ❤ by GitHub