147. Insertion Sort List, 147 insertion

147. Insertion Sort List, 147 insertion

Sort a linked list using insertion sort.

 

Use an auxiliary pointer as the header to avoid the boundary situation when the head is changed.

 

1/** 2 * Definition for singly-linked list. 3 * struct ListNode {4 * int val; 5 * ListNode * next; 6 * ListNode (int x): val (x), next (NULL) {} 7 *}; 8 */9 class Solution {10 public: 11 ListNode * insertionSortList (ListNode * head) {12 if (head = NULL) {13 return head; 14} 15 16 ListNode * helper = new ListNode (0); 17 ListNode * pre = helper; 18 ListNode * cur = head; 19 20 while (cur! = NULL) {21 ListNode * next = cur-> next; 22 // save head position 23 pre = helper; 24 while (pre-> next! = NULL & pre-> next-> val <cur-> val) {25 pre = pre-> next; 26} 27 // insert 28 cur-> next = pre-> next; 29 pre-> next = cur; 30 // restore 31 32 cur = next; 33} 34 return helper-> next; 35} 36 };