LinkedList in Leetcode
Leetcode 206. Reverse Linked List
Leetcode 206. Reverse Linked List
Reverse a singly linked list.
class Solution {
public:
ListNode* reverseList(ListNode* head) {
if (!head || !head->next)
return head;
ListNode* newHead = reverseList(head->next);
head->next->next = head;
head->next = NULL;
return newHead;
}
};
92. Reverse Linked List II]
Reverse a linked list from position m to n. Do it in-place and in one-pass.
For example:
Given 1->2->3->4->5->NULL, m = 2 and n = 4,
return 1->4->3->2->5->NULL.
class Solution {
public:
ListNode* reverseBetween(ListNode* head, int m, int n) {
ListNode* prehead = new ListNode(0);
prehead->next = head;
ListNode* tail = prehead;
n -= m;
while(--m > 0) tail = tail->next;
ListNode* curr = tail->next;
while(n-- > 0){ // pull one out to tail
ListNode* temp = curr->next;
curr->next = temp->next;
temp->next = tail->next; // easy to make mistake
tail->next = temp;
}
return prehead->next;
}
};