【LBLD】递归魔法：反转单链表
递归反转整个链表
/**
* 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 || head->next == nullptr) {
return head;
}
ListNode *last = reverseList(head->next);
head->next->next = head;
head->next = nullptr;
return last;
}
};
反转链表的一部分
/**
* 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* successor = nullptr;
ListNode* reverseN(ListNode* head, int n) {
if (n == 1) {
successor = head->next;
return head;
}
ListNode *last = reverseN(head->next, n-1);
head->next->next = head;
head->next = successor;
return last;
}
ListNode* reverseBetween(ListNode* head, int left, int right) {
if (left == 1) {
return reverseN(head, right);
}
head->next = reverseBetween(head->next, left-1, right-1);
return head;
}
};