leetcode-206-Reverse-Linked-List

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描述

Reverse a singly linked list.

分析

meh，画图。

解决方案1(Python)

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# Definition for singly-linked list.
# class ListNode(object):
#     def __init__(self, x):
#         self.val = x
#         self.next = None

class Solution(object):
    def reverseList(self, head):
        """
        :type head: ListNode
        :rtype: ListNode
        """
        if head is None:
            return 
        result_node = [None, head]
        while True:
            if result_node[-1].next is not None:
                result_node.append(result_node[-1].next)
            else:
                break
        for i in range(1, len(result_node)):
            result_node[i].next = result_node[i-1]
        return result_node[-1]

解决方案2(C++)

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/**
 * 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 && head->next != NULL) {
            ListNode* pivot = head;
            ListNode* frontier = NULL;
            while(pivot!=NULL && pivot->next!=NULL){
                frontier = pivot->next;
                pivot->next = pivot->next->next;
                frontier->next = head;
                head = frontier;
            }
        }
        return head;
    }
};

解决方案3(Java)

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/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) { val = x; }
 * }
 */
public class Solution {
    public ListNode reverseList(ListNode head) {
        if(head != null && head.next != null) {
            ListNode pivot = head;
            ListNode frontier = null;
            while(pivot!=null && pivot.next!=null){
                frontier = pivot.next;
                pivot.next = pivot.next.next;
                frontier.next = head;
                head = frontier;
            }
        }
        return head;
    }
}

解决方案4（Golang）

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/**
 * Definition for singly-linked list.
 * type ListNode struct {
 *     Val int
 *     Next *ListNode
 * }
 */
func reverseList(head *ListNode) *ListNode {
    var pre *ListNode = nil
    
    current := head
    for nil != current {
        now := current.Next
        current.Next = pre
        pre = current
        current = now
    }
    return pre
}

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