Created
July 2, 2020 21:56
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Java merge sort solution of Sort List https://leetcode.com/problems/sort-list/
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public class Solution { | |
public ListNode sortList(ListNode head) { | |
if (head == null || head.next == null) | |
return head; | |
// step 1. cut the list to two halves | |
ListNode prev = null, slow = head, fast = head; | |
while (fast != null && fast.next != null) { | |
prev = slow; | |
slow = slow.next; | |
fast = fast.next.next; | |
} | |
prev.next = null; | |
// step 2. sort each half | |
ListNode l1 = sortList(head); | |
ListNode l2 = sortList(slow); | |
// step 3. merge l1 and l2 | |
return merge(l1, l2); | |
} | |
ListNode merge(ListNode l1, ListNode l2) { | |
ListNode l = new ListNode(0), p = l; | |
while (l1 != null && l2 != null) { | |
if (l1.val < l2.val) { | |
p.next = l1; | |
l1 = l1.next; | |
} else { | |
p.next = l2; | |
l2 = l2.next; | |
} | |
p = p.next; | |
} | |
if (l1 != null) | |
p.next = l1; | |
if (l2 != null) | |
p.next = l2; | |
return l.next; | |
} | |
} |
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