LeetCode 148. Sort List
Solution1:我的答案
很多递归
/**
* Definition for singly-linked list.
* struct ListNode {
* int val;
* ListNode *next;
* ListNode(int x) : val(x), next(NULL) {}
* };
*/
class Solution {
public:
ListNode* sortList(ListNode* head) {
if (!head) return NULL;
if (!head->next) return head;
ListNode *slow = head, *fast = head;
while (fast->next && fast->next->next) {//快慢指针找链表中点
slow = slow->next;
fast = fast->next->next;
}
fast = slow->next;//fast重新定义为第二段链表的起点
slow->next = NULL;//两条链表断开
ListNode *l1 = sortList(head);
ListNode *l2 = sortList(fast);
return mergetwolists(l1, l2);
}
ListNode* mergetwolists (ListNode* l1, ListNode* l2) {//合并两个有序链表的代码重用度很高啊
if (!l1) return l2;
if (!l2) return l1;
ListNode *dummy = new ListNode(-1), *cur = dummy;
while (l1 && l2) {
if (l1->val <= l2->val) {
cur->next = l1;
l1 = l1->next;
} else {
cur->next = l2;
l2 = l2->next;
}
cur = cur->next;
}
if (l1) cur->next = l1;
if (l2) cur->next = l2;
return dummy->next;
}
};