Skip to content

Navigation Menu

Sign in
Appearance settings

Search code, repositories, users, issues, pull requests...

Provide feedback

We read every piece of feedback, and take your input very seriously.

Saved searches

Use saved searches to filter your results more quickly
Sign up
Appearance settings

Commit b9ac7fe

Browse files
check in source code
1 parent 76279a4 commit b9ac7fe

File tree

2 files changed

+292
-0
lines changed

2 files changed

+292
-0
lines changed
Lines changed: 146 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,146 @@
1+
using System;
2+
using System.Collections.Generic;
3+
using System.Linq;
4+
using System.Text;
5+
using System.Threading.Tasks;
6+
7+
namespace Leetcode_234_Palindrome_Linked_List
8+
{
9+
/// <summary>
10+
/// Leetcode 234 Palindrome linked list
11+
/// https://leetcode.com/problems/palindrome-linked-list/description/
12+
/// Could you do it in O(n) time and O(1) space?
13+
/// </summary>
14+
class Program
15+
{
16+
public class ListNode {
17+
public int val;
18+
public ListNode next;
19+
public ListNode(int x) { val = x; }
20+
}
21+
22+
static void Main(string[] args)
23+
{
24+
RunTestcase();
25+
}
26+
27+
public static void RunTestcase()
28+
{
29+
var head = new ListNode(1);
30+
var node2 = new ListNode(2);
31+
32+
head.next = node2;
33+
34+
var result = IsPalindrome(head);
35+
}
36+
37+
public static void RunTestcase2()
38+
{
39+
var head = new ListNode(1);
40+
var node2 = new ListNode(2);
41+
var node3 = new ListNode(2);
42+
var node4 = new ListNode(1);
43+
44+
head.next = node2;
45+
node2.next = node3;
46+
node3.next = node4;
47+
48+
var result = IsPalindrome(head);
49+
}
50+
51+
/// <summary>
52+
/// design function using three API
53+
/// 1. reverse linked list
54+
/// 2. get length of linked list
55+
/// 3. get kth linked list node
56+
/// </summary>
57+
/// <param name="head"></param>
58+
/// <returns></returns>
59+
public static bool IsPalindrome(ListNode head)
60+
{
61+
if (head == null)
62+
return true;
63+
64+
if (head.next == null)
65+
return true;
66+
67+
var length = getLinkedListLength(head);
68+
var isEven = length % 2 == 0;
69+
var back = head;
70+
var front = getNodeGivenK(head, length/ 2);
71+
if (!isEven)
72+
{
73+
front = front.next;
74+
}
75+
76+
var reversed = reverseLinkedList(front);
77+
78+
// compare two linked list one element a time
79+
var index = 0;
80+
while (index < length / 2)
81+
{
82+
if (back.val != reversed.val)
83+
return false;
84+
85+
back = back.next;
86+
reversed = reversed.next;
87+
index++;
88+
}
89+
90+
return true;
91+
}
92+
93+
/// <summary>
94+
/// reverse a linked list using O(N) time and O(1) space
95+
/// </summary>
96+
/// <param name="head"></param>
97+
private static ListNode reverseLinkedList(ListNode head)
98+
{
99+
if (head == null)
100+
return null;
101+
if (head.next == null)
102+
return head;
103+
104+
var next = head.next;
105+
var reversed = reverseLinkedList(next);
106+
107+
head.next = null;
108+
next.next = head;
109+
110+
return reversed;
111+
}
112+
113+
private static ListNode getNodeGivenK(ListNode head, int k)
114+
{
115+
if (k == 0)
116+
return head;
117+
118+
int index = 0;
119+
var iterate = head;
120+
while (index < k)
121+
{
122+
iterate = iterate.next;
123+
index++;
124+
}
125+
126+
return iterate;
127+
}
128+
129+
private static int getLinkedListLength(ListNode head)
130+
{
131+
if (head == null)
132+
return 0;
133+
134+
var index = 0;
135+
var iterate = head;
136+
while (iterate != null)
137+
{
138+
index++;
139+
140+
iterate = iterate.next;
141+
}
142+
143+
return index;
144+
}
145+
}
146+
}

‎Leetcode 234 Palindrome Linked List.cs

Lines changed: 146 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,146 @@
1+
using System;
2+
using System.Collections.Generic;
3+
using System.Linq;
4+
using System.Text;
5+
using System.Threading.Tasks;
6+
7+
namespace Leetcode_234_Palindrome_Linked_List
8+
{
9+
/// <summary>
10+
/// Leetcode 234 Palindrome linked list
11+
/// https://leetcode.com/problems/palindrome-linked-list/description/
12+
/// Could you do it in O(n) time and O(1) space?
13+
/// </summary>
14+
class Program
15+
{
16+
public class ListNode {
17+
public int val;
18+
public ListNode next;
19+
public ListNode(int x) { val = x; }
20+
}
21+
22+
static void Main(string[] args)
23+
{
24+
RunTestcase();
25+
}
26+
27+
public static void RunTestcase()
28+
{
29+
var head = new ListNode(1);
30+
var node2 = new ListNode(2);
31+
32+
head.next = node2;
33+
34+
var result = IsPalindrome(head);
35+
}
36+
37+
public static void RunTestcase2()
38+
{
39+
var head = new ListNode(1);
40+
var node2 = new ListNode(2);
41+
var node3 = new ListNode(2);
42+
var node4 = new ListNode(1);
43+
44+
head.next = node2;
45+
node2.next = node3;
46+
node3.next = node4;
47+
48+
var result = IsPalindrome(head);
49+
}
50+
51+
/// <summary>
52+
/// design function using three API
53+
/// 1. reverse linked list
54+
/// 2. get length of linked list
55+
/// 3. get kth linked list node
56+
/// </summary>
57+
/// <param name="head"></param>
58+
/// <returns></returns>
59+
public static bool IsPalindrome(ListNode head)
60+
{
61+
if (head == null)
62+
return true;
63+
64+
if (head.next == null)
65+
return true;
66+
67+
var length = getLinkedListLength(head);
68+
var isEven = length % 2 == 0;
69+
var back = head;
70+
var front = getNodeGivenK(head, length/ 2);
71+
if (!isEven)
72+
{
73+
front = front.next;
74+
}
75+
76+
var reversed = reverseLinkedList(front);
77+
78+
// compare two linked list one element a time
79+
var index = 0;
80+
while (index < length / 2)
81+
{
82+
if (back.val != reversed.val)
83+
return false;
84+
85+
back = back.next;
86+
reversed = reversed.next;
87+
index++;
88+
}
89+
90+
return true;
91+
}
92+
93+
/// <summary>
94+
/// reverse a linked list using O(N) time and O(1) space
95+
/// </summary>
96+
/// <param name="head"></param>
97+
private static ListNode reverseLinkedList(ListNode head)
98+
{
99+
if (head == null)
100+
return null;
101+
if (head.next == null)
102+
return head;
103+
104+
var next = head.next;
105+
var reversed = reverseLinkedList(next);
106+
107+
head.next = null;
108+
next.next = head;
109+
110+
return reversed;
111+
}
112+
113+
private static ListNode getNodeGivenK(ListNode head, int k)
114+
{
115+
if (k == 0)
116+
return head;
117+
118+
int index = 0;
119+
var iterate = head;
120+
while (index < k)
121+
{
122+
iterate = iterate.next;
123+
index++;
124+
}
125+
126+
return iterate;
127+
}
128+
129+
private static int getLinkedListLength(ListNode head)
130+
{
131+
if (head == null)
132+
return 0;
133+
134+
var index = 0;
135+
var iterate = head;
136+
while (iterate != null)
137+
{
138+
index++;
139+
140+
iterate = iterate.next;
141+
}
142+
143+
return index;
144+
}
145+
}
146+
}

0 commit comments

Comments
(0)

AltStyle によって変換されたページ (->オリジナル) /