标签：des style blog color 使用 java ar strong art
Merge Two Sorted Lists:
Merge two sorted linked lists and return it as a new list. The new list should be made by splicing together the nodes of the first two lists.
两个排好序的链表拼接，只要用两个指针遍历链表即可. 可以借助一个helper指针来进行开头的合并。如果有一个遍历完，则直接把另一个链表指针之后的部分全部接在后面：
1 public ListNode mergeTwoLists(ListNode l1, ListNode l2) { 2 ListNode helper = new ListNode(0); 3 ListNode cur1 = l1; 4 ListNode cur2 = l2; 5 ListNode cur = helper; 6 while(cur1!=null || cur2!=null) 7 { 8 if(cur1==null) 9 { 10 cur.next = cur2; 11 break; 12 } 13 if(cur2==null) 14 { 15 cur.next = cur1; 16 break; 17 } 18 if(cur1.val<=cur2.val) 19 { 20 cur.next = cur1; 21 cur1=cur1.next; 22 } 23 else 24 { 25 cur.next = cur2; 26 cur2=cur2.next; 27 } 28 cur=cur.next; 29 } 30 return helper.next; 31 }
Sort List:
Sort a linked list in O(n log n) time using constant space complexity.
有了Merged Two Sorted Lists的基础，这题就很好写了。提到O(nlogn)的排序算法，马上想到快排和合并排序，不过快排不稳定而且对于链表来说交换不方便，所以还是决定采用merge sort.
对于链表，merge sort中的split过程可以使用快慢指针实现，比较简单易懂：
1 public ListNode sortList(ListNode head) { 2 return mergeSort(head); 3 } 4 5 public ListNode mergeSort(ListNode start) 6 { 7 if(start==null) return null; 8 if(start.next==null) return start; 9 10 ListNode slow = start; 11 ListNode fast = start; 12 while(fast!=null && fast.next!=null && fast.next.next!=null) 13 { 14 slow = slow.next; 15 fast = fast.next.next; 16 } 17 ListNode second = slow.next; 18 slow.next = null; 19 return mergeTwoLists(mergeSort(start), mergeSort(second)); 20 } 21 public ListNode mergeTwoLists(ListNode l1, ListNode l2) { 22 ListNode helper = new ListNode(0); 23 ListNode cur1 = l1; 24 ListNode cur2 = l2; 25 ListNode cur = helper; 26 while(cur1!=null || cur2!=null) 27 { 28 if(cur1==null) 29 { 30 cur.next = cur2; 31 break; 32 } 33 if(cur2==null) 34 { 35 cur.next = cur1; 36 break; 37 } 38 if(cur1.val<=cur2.val) 39 { 40 cur.next = cur1; 41 cur1=cur1.next; 42 } 43 else 44 { 45 cur.next = cur2; 46 cur2=cur2.next; 47 } 48 cur=cur.next; 49 } 50 return helper.next; 51 }
[Leetcode][JAVA] Merge Two Sorted Lists & Sort List
标签：des style blog color 使用 java ar strong art
原文地址：http://www.cnblogs.com/splash/p/3972013.html
