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Add palindrome singly linkedlist optimised approach (#5617)

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This commit is contained in:
Nandini Pandey
2024-10-08 00:28:17 +05:30
committed by GitHub
parent 4a5bf39f8e
commit 6868bf8ba0
2 changed files with 115 additions and 0 deletions
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43
src/main/java/com/thealgorithms/misc/PalindromeSinglyLinkedList.java
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@ -30,4 +30,47 @@ public final class PalindromeSinglyLinkedList {
return true;
}
// Optimised approach with O(n) time complexity and O(1) space complexity
public static boolean isPalindromeOptimised(Node head) {
if (head == null || head.next == null) {
return true;
}
Node slow = head;
Node fast = head;
while (fast != null && fast.next != null) {
slow = slow.next;
fast = fast.next.next;
}
Node midNode = slow;
Node prevNode = null;
Node currNode = midNode;
Node nextNode;
while (currNode != null) {
nextNode = currNode.next;
currNode.next = prevNode;
prevNode = currNode;
currNode = nextNode;
}
Node left = head;
Node right = prevNode;
while (left != null && right != null) {
if (left.val != right.val) {
return false;
}
right = right.next;
left = left.next;
}
return true;
}
static class Node {
int val;
Node next;
Node(int val) {
this.val = val;
this.next = null;
}
}
}

72
src/test/java/com/thealgorithms/misc/PalindromeSinglyLinkedListTest.java
View File

@ -7,6 +7,8 @@ import com.thealgorithms.datastructures.lists.SinglyLinkedList;
import org.junit.jupiter.api.Test;
public class PalindromeSinglyLinkedListTest {
// Stack-based tests
@Test
public void testWithEmptyList() {
assertTrue(PalindromeSinglyLinkedList.isPalindrome(new SinglyLinkedList()));
@ -67,4 +69,74 @@ public class PalindromeSinglyLinkedListTest {
exampleList.insert(20);
assertFalse(PalindromeSinglyLinkedList.isPalindrome(exampleList));
}
// Optimized approach tests
@Test
public void testOptimisedWithEmptyList() {
assertTrue(PalindromeSinglyLinkedList.isPalindromeOptimised(null));
}
@Test
public void testOptimisedWithSingleElement() {
PalindromeSinglyLinkedList.Node node = new PalindromeSinglyLinkedList.Node(100);
assertTrue(PalindromeSinglyLinkedList.isPalindromeOptimised(node));
}
@Test
public void testOptimisedWithOddLengthPositive() {
PalindromeSinglyLinkedList.Node node1 = new PalindromeSinglyLinkedList.Node(1);
PalindromeSinglyLinkedList.Node node2 = new PalindromeSinglyLinkedList.Node(2);
PalindromeSinglyLinkedList.Node node3 = new PalindromeSinglyLinkedList.Node(1);
node1.next = node2;
node2.next = node3;
assertTrue(PalindromeSinglyLinkedList.isPalindromeOptimised(node1));
}
@Test
public void testOptimisedWithOddLengthPositive2() {
PalindromeSinglyLinkedList.Node node1 = new PalindromeSinglyLinkedList.Node(3);
PalindromeSinglyLinkedList.Node node2 = new PalindromeSinglyLinkedList.Node(2);
PalindromeSinglyLinkedList.Node node3 = new PalindromeSinglyLinkedList.Node(1);
PalindromeSinglyLinkedList.Node node4 = new PalindromeSinglyLinkedList.Node(2);
PalindromeSinglyLinkedList.Node node5 = new PalindromeSinglyLinkedList.Node(3);
node1.next = node2;
node2.next = node3;
node3.next = node4;
node4.next = node5;
assertTrue(PalindromeSinglyLinkedList.isPalindromeOptimised(node1));
}
@Test
public void testOptimisedWithEvenLengthPositive() {
PalindromeSinglyLinkedList.Node node1 = new PalindromeSinglyLinkedList.Node(10);
PalindromeSinglyLinkedList.Node node2 = new PalindromeSinglyLinkedList.Node(20);
PalindromeSinglyLinkedList.Node node3 = new PalindromeSinglyLinkedList.Node(20);
PalindromeSinglyLinkedList.Node node4 = new PalindromeSinglyLinkedList.Node(10);
node1.next = node2;
node2.next = node3;
node3.next = node4;
assertTrue(PalindromeSinglyLinkedList.isPalindromeOptimised(node1));
}
@Test
public void testOptimisedWithOddLengthNegative() {
PalindromeSinglyLinkedList.Node node1 = new PalindromeSinglyLinkedList.Node(1);
PalindromeSinglyLinkedList.Node node2 = new PalindromeSinglyLinkedList.Node(2);
PalindromeSinglyLinkedList.Node node3 = new PalindromeSinglyLinkedList.Node(2);
node1.next = node2;
node2.next = node3;
assertFalse(PalindromeSinglyLinkedList.isPalindromeOptimised(node1));
}
@Test
public void testOptimisedWithEvenLengthNegative() {
PalindromeSinglyLinkedList.Node node1 = new PalindromeSinglyLinkedList.Node(10);
PalindromeSinglyLinkedList.Node node2 = new PalindromeSinglyLinkedList.Node(20);
PalindromeSinglyLinkedList.Node node3 = new PalindromeSinglyLinkedList.Node(20);
PalindromeSinglyLinkedList.Node node4 = new PalindromeSinglyLinkedList.Node(20);
node1.next = node2;
node2.next = node3;
node3.next = node4;
assertFalse(PalindromeSinglyLinkedList.isPalindromeOptimised(node1));
}
}