[LeetCode]97. Reorder List链表重排序
Given a singly linked list L: L0→L1→…→Ln-1→Ln,
reorder it to: L0→Ln→L1→Ln-1→L2→Ln-2→…
You must do this in-place without altering the nodes' values.
For example,
Given {1,2,3,4}
, reorder it to {1,4,2,3}
.
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解法:仔细分析题目意思,一个简单的方法就是将后半部分链表先逆转,然后插入到前半部分。因此可以写出如下代码:
/** * Definition for singly-linked list. * struct ListNode { * int val; * ListNode *next; * ListNode(int x) : val(x), next(NULL) {} * }; */ class Solution { public: void reorderList(ListNode* head) { if(head == NULL || head->next == NULL) return; ListNode *slow = head, *fast = head; while(fast->next != NULL && fast->next->next != NULL) { slow = slow->next; fast = fast->next->next; } ListNode* head1 = head; ListNode* head2 = slow->next; head2 = reverseList(head2); slow->next = NULL; while(head2 != NULL) { ListNode *next1 = head1->next, *next2 = head2->next; head1->next = head2; head2->next = next1; head1 = next1; head2 = next2; } } private: ListNode* reverseList(ListNode* head) { ListNode* rHead = NULL; ListNode* curr = head; ListNode* pTail = NULL; while(curr != NULL) { ListNode* pNext = curr->next; if(pNext == NULL) rHead = curr; curr->next = pTail; pTail = curr; curr = pNext; } return rHead; } };