-
-
Notifications
You must be signed in to change notification settings - Fork 797
/
PartitionList.java
74 lines (64 loc) · 2.24 KB
/
PartitionList.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
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
/*
* Copyright (C) 2014 Pedro Vicente Gómez Sánchez.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package com.github.pedrovgs.problem60;
import com.github.pedrovgs.linkedlist.ListNode;
/**
* Write code to partition a linked list around a value x, such that all nodes less than x come
* before after nodes greater than or equal to x.
*
* @author Pedro Vicente Gómez Sánchez.
*/
public class PartitionList {
/**
* Iterative algorithm to solve this problem. Using two pointer to the element before the value
* and after the value we are going to create two list and merge it at the end of this algorithm.
* The complexity order is equals to O(N) in time terms and O(1) in space terms because we are
* not
* using any auxiliary data structure to solve this problem.
*/
public ListNode<Integer> split(ListNode<Integer> list, int x) {
validateInput(list);
ListNode<Integer> before = null;
ListNode<Integer> after = null;
while (list != null) {
ListNode<Integer> next = list.getNext();
if (list.getData() < x) {
list.setNext(before);
before = list;
} else {
list.setNext(after);
after = list;
}
list = next;
}
if (before == null) {
return after;
}
ListNode<Integer> result = mergeLists(before, after);
return result;
}
private ListNode<Integer> mergeLists(ListNode<Integer> before, ListNode<Integer> after) {
ListNode<Integer> result = before;
while (before.getNext() != null) {
before = before.getNext();
}
before.setNext(after);
return result;
}
private void validateInput(ListNode<Integer> list) {
if (list == null) throw new IllegalArgumentException("You can't pass a null list as argument.");
}
}