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148_sortList.java
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148_sortList.java
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/**
* Definition for singly-linked list.
* public class ListNode {
* int val;
* ListNode next;
* ListNode() {}
* ListNode(int val) { this.val = val; }
* ListNode(int val, ListNode next) { this.val = val; this.next = next; }
* }
*/
class Solution {
public ListNode sortList(ListNode head) {
if(head == null || head.next == null) return head;
ListNode[] nodes = split(head);
ListNode l = sortList(nodes[0]);
ListNode r = sortList(nodes[1]);
return merge(l,r);
}
public ListNode[] split(ListNode head){
ListNode dummy = new ListNode(0);
dummy.next = head; //Add dummy in front to make sure slow would be the mid!
ListNode fast = dummy;
ListNode slow = dummy;
while(fast != null && fast.next != null){
fast = fast.next.next;
slow = slow.next;
}
ListNode r = slow.next;
ListNode l = dummy.next;
slow.next = null;
ListNode[] res = new ListNode[2];
res[0] = l;
res[1] = r;
return res;
}
public ListNode merge(ListNode l, ListNode r){
ListNode dummy = new ListNode(0);
ListNode run = dummy;
while(l != null && r != null){
if(l.val < r.val){
run.next = new ListNode(l.val);
l = l.next;
} else{
run.next = new ListNode(r.val);
r = r.next;
}
run = run.next;
}
if(l != null){
run.next = l;
}
if(r != null){
run.next = r;
}
return dummy.next;
}
}