92. Reverse Linked List II
1.問題
反轉linked list m~n的順序

2.想法
提問
function header, parameter
test input
說明想法
讓*pre為開始反轉的前一個指標
*cur為開始反轉的第一個指標
測試計算複雜度: O(n^2) ?
3.程式碼
/**
* Definition for singly-linked list.
* struct ListNode {
* int val;
* ListNode *next;
* ListNode(int x) : val(x), next(NULL) {}
* };
*/
class Solution {
public:
ListNode* reverseBetween(ListNode* head, int m, int n) {
if (m < 1 || m >= n || !head) {
return head;
}
ListNode *newNode = new ListNode(0);
newNode->next = head;
head = newNode;
for (int i = 0; i < m - 1; i++) {
head = head->next;
}
ListNode *pre = head->next, *cur = pre->next;
for (int i = 0; i < n - m; i++) {
ListNode *next = cur->next;
cur->next = pre;
pre = cur;
cur = next;
}
head->next->next = cur;
head->next = pre;
return newNode->next;
}
};
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