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LC206reverseLinkedList.cpp
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LC206reverseLinkedList.cpp
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/**
* Definition for singly-linked list.
* struct ListNode {
* int val;
* ListNode *next;
* ListNode() : val(0), next(nullptr) {}
* ListNode(int x) : val(x), next(nullptr) {}
* ListNode(int x, ListNode *next) : val(x), next(next) {}
* };
*/
class Solution {
public:
ListNode* reverseList(ListNode* head) {
if (head == nullptr) return head;
ListNode *nextnode, *prenode = nullptr, *currnode = head;
while (currnode) {
nextnode = currnode->next;
currnode->next = prenode;
prenode = currnode;
currnode = nextnode;
}
return prenode;
}
};
class Solution2 {
public:
ListNode* reverseList(ListNode* head) {
if (head == nullptr) return head;
ListNode *nextnode, *nextnextnode;
if (head->next) {
nextnode = head->next;
head->next = nullptr;
while (nextnode->next != nullptr) {
nextnextnode = nextnode->next;
nextnode->next = head;
head = nextnode;
nextnode = nextnextnode;
}
nextnode->next = head;
head = nextnode;
}
return head;
}
};