-
Notifications
You must be signed in to change notification settings - Fork 13
/
MergeTwoLists21.java
46 lines (41 loc) · 1.07 KB
/
MergeTwoLists21.java
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
package Leetcode;
public class MergeTwoLists21 {
/** Method 1:Recursion, Time: O(N+M), Space:O(N+M)**/
public ListNode mergeTwoLists(ListNode l1, ListNode l2) {
if(l1 == null) {
return l2;
} else if(l2 == null) {
return l1;
} else if(l1.val < l2.val) {
l1.next = mergeTwoLists(l1.next, l2);
return l1;
} else {
l2.next = mergeTwoLists(l1, l2.next);
return l2;
}
}
/** Method 2:Iteration + Dummy Node, Time: O(N+M), Space:O(N+M)**/
public ListNode mergeTwoLists2(ListNode l1, ListNode l2) {
ListNode dummy = new ListNode(-1);
ListNode pre = dummy;
while(l1 != null && l2 != null) {
if(l1.val < l2.val) {
pre.next = l1;
l1 = l1.next;
} else {
pre.next = l2;
l2 = l2.next;
}
pre = pre.next;
}
pre.next = l1 == null? l2: l1;
return dummy.next;
}
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; }
}
}