#力扣：206. 反转链表@FDDLC

206. 反转链表

一、Java

class Solution {
    public ListNode reverseList(ListNode head) {
        if (head == null) return null;
        ListNode pre = null, cur = head, next = head.next;
        while (next != null) {
            cur.next = pre;
            pre = cur;
            cur = next;
            next = cur.next;
        }
        cur.next = pre;
        return cur;
    }
}

class Solution {
    public ListNode reverseList(ListNode head) {
        ListNode pre = null, cur = head, next;
        while (cur != null) {
            next = cur.next;
            cur.next = pre;
            pre = cur;
            cur = next;
        }
        return pre;
    }
}

class Solution {
    public ListNode reverseList(ListNode head) {
        if (head == null || head.next == null) return head;
        ListNode next = head.next, newHead = reverseList(next);
        head.next = null;
        next.next = head;
        return newHead;
    }
}

class Solution {
    public ListNode reverseList(ListNode head) {
        if (head == null || head.next == null) return head;
        ListNode newHead = reverseList(head.next);
        head.next.next = head;
        head.next = null;
        return newHead;
    }
}

二、C++

class Solution {
public:
    ListNode* reverseList(ListNode* head) {
        ListNode *pre = nullptr, *cur = head, *next;
        while (cur != nullptr) {
            next = cur->next;
            cur->next = pre;
            pre = cur;
            cur = next;
        }
        return pre;
    }
};

class Solution {
public:
    ListNode* reverseList(ListNode* head) {
        if (head == nullptr || head->next == nullptr) return head;
        ListNode *newHead = reverseList(head->next);
        head->next->next = head;
        head->next = nullptr;
        return newHead;
    }
};

三、Python

class Solution:
    def reverseList(self, head: Optional[ListNode]) -> Optional[ListNode]:
        pre, cur, next = None, head, None
        while cur is not None:
            next = cur.next
            cur.next = pre
            pre = cur
            cur = next
        return pre

class Solution:
    def reverseList(self, head: Optional[ListNode]) -> Optional[ListNode]:
        if head is None or head.next is None:
            return head
        newHead = self.reverseList(head.next)
        head.next.next = head
        head.next = None
        return newHead

四、JavaScript

var reverseList = function (head) {
    let pre = null, cur = head, next;
    while (cur != null) {
        next = cur.next;
        cur.next = pre;
        pre = cur;
        cur = next;
    }
    return pre;
};

var reverseList = function (head) {
    if (head == null || head.next == null) return head;
    let newHead = reverseList(head.next);
    head.next.next = head;
    head.next = null;
    return newHead;
};

五、Go

func reverseList(head *ListNode) *ListNode {
	var pre *ListNode
	cur := head
	for cur != nil {
		next := cur.Next
		cur.Next = pre
		pre = cur
		cur = next
	}
	return pre
}

func reverseList(head *ListNode) *ListNode {
	if head == nil || head.Next == nil {
		return head
	}
	newHead := reverseList(head.Next)
	head.Next.Next = head
	head.Next = nil
	return newHead
}