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Sort-List-148.cpp
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Sort-List-148.cpp
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/**
* 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 == NULL || head->next == NULL){
return head;
}
ListNode* fast = head;
ListNode* slow = head;
while(fast->next && fast->next->next){
fast = fast->next->next;
slow = slow->next;
}
fast = slow->next;
slow->next = NULL;
ListNode* p1 = sortList(head);
ListNode* p2 = sortList(fast);
return merge(p1, p2);
}
ListNode* merge(ListNode* l1, ListNode* l2){
/*if (!l1){
return l2;
}else if (!l2){
return l1;
}else if (!l1 && !l2){
return NULL;
}*/
ListNode helper(0);
ListNode* p = &helper;
while(l1 && l2){
if (l1->val < l2->val){
p->next = l1;
l1 = l1->next;
}else {
p->next = l2;
l2 = l2->next;
}
p = p->next;
}
if (!l1){
p->next = l2;
}else {
p->next = l1;
}
return helper.next;
}
};