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BAEL-1123 - Testing Linked List for Cycles - deep20jain@gmail.com (#2525)

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* Adding node and cycle detection by hashing

* Adding implementation for all algorithms for cycle detection and removal

* Applying formatting rules
This commit is contained in:
deep20jain 2017-09-04 01:50:25 +05:30 committed by Zeger Hendrikse
parent 4baaf9f984
commit d8398caaa2
14 changed files with 432 additions and 0 deletions
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38
algorithms/src/main/java/com/baeldung/algorithms/linkedlist/CycleDetectionBruteForce.java Normal file
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package com.baeldung.algorithms.linkedlist;
public class CycleDetectionBruteForce {
public static <T> boolean detectCycle(Node<T> head) {
if (head == null) {
return false;
}
Node<T> it1 = head;
int nodesTraversedByOuter = 0;
while (it1 != null && it1.next != null) {
it1 = it1.next;
nodesTraversedByOuter++;
int x = nodesTraversedByOuter;
Node<T> it2 = head;
int noOfTimesCurrentNodeVisited = 0;
while (x > 0) {
it2 = it2.next;
if (it2 == it1) {
noOfTimesCurrentNodeVisited++;
}
if (noOfTimesCurrentNodeVisited == 2) {
return true;
}
x--;
}
}
return false;
}
}

25
algorithms/src/main/java/com/baeldung/algorithms/linkedlist/CycleDetectionByFastAndSlowIterators.java Normal file
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package com.baeldung.algorithms.linkedlist;
public class CycleDetectionByFastAndSlowIterators {
public static <T> boolean detectCycle(Node<T> head) {
if (head == null) {
return false;
}
Node<T> slow = head;
Node<T> fast = head;
while (fast != null && fast.next != null) {
slow = slow.next;
fast = fast.next.next;
if (slow == fast) {
return true;
}
}
return false;
}
}

27
algorithms/src/main/java/com/baeldung/algorithms/linkedlist/CycleDetectionByHashing.java Normal file
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package com.baeldung.algorithms.linkedlist;
import java.util.HashSet;
import java.util.Set;
public class CycleDetectionByHashing {
public static <T> boolean detectCycle(Node<T> head) {
if (head == null) {
return false;
}
Set<Node<T>> set = new HashSet<>();
Node<T> node = head;
while (node != null) {
if (set.contains(node)) {
return true;
}
set.add(node);
node = node.next;
}
return false;
}
}

61
algorithms/src/main/java/com/baeldung/algorithms/linkedlist/CycleRemovalBruteForce.java Normal file
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package com.baeldung.algorithms.linkedlist;
public class CycleRemovalBruteForce {
public static <T> boolean detectAndRemoveCycle(Node<T> head) {
if (head == null) {
return false;
}
Node<T> slow = head;
Node<T> fast = head;
while (fast != null && fast.next != null) {
slow = slow.next;
fast = fast.next.next;
if (slow == fast) {
removeCycle(slow, head);
return true;
}
}
return false;
}
private static <T> void removeCycle(Node<T> loopNodeParam, Node<T> head) {
Node<T> it = head;
while (it != null) {
if (isNodeReachableFromLoopNode(it, loopNodeParam)) {
Node<T> loopStart = it;
findEndNodeAndBreakCycle(loopStart);
break;
}
it = it.next;
}
}
private static <T> boolean isNodeReachableFromLoopNode(Node<T> it, Node<T> loopNodeParam) {
Node<T> loopNode = loopNodeParam;
while (loopNode.next != loopNodeParam) {
if (it == loopNode) {
return true;
}
loopNode = loopNode.next;
}
return false;
}
private static <T> void findEndNodeAndBreakCycle(Node<T> loopStartParam) {
Node<T> loopStart = loopStartParam;
while (loopStart.next != loopStartParam) {
loopStart = loopStart.next;
}
loopStart.next = null;
}
}

55
algorithms/src/main/java/com/baeldung/algorithms/linkedlist/CycleRemovalByCountingLoopNodes.java Normal file
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package com.baeldung.algorithms.linkedlist;
public class CycleRemovalByCountingLoopNodes {
public static <T> boolean detectAndRemoveCycle(Node<T> head) {
if (head == null) {
return false;
}
Node<T> slow = head;
Node<T> fast = head;
while (fast != null && fast.next != null) {
slow = slow.next;
fast = fast.next.next;
if (slow == fast) {
int cycleLength = calculateCycleLength(slow);
removeCycle(head, cycleLength);
return true;
}
}
return false;
}
private static <T> void removeCycle(Node<T> head, int cycleLength) {
Node<T> cycleLengthAdvancedIterator = head;
Node<T> it = head;
for (int i = 0; i < cycleLength; i++) {
cycleLengthAdvancedIterator = cycleLengthAdvancedIterator.next;
}
while (it.next != cycleLengthAdvancedIterator.next) {
it = it.next;
cycleLengthAdvancedIterator = cycleLengthAdvancedIterator.next;
}
cycleLengthAdvancedIterator.next = null;
}
private static <T> int calculateCycleLength(Node<T> loopNodeParam) {
Node<T> loopNode = loopNodeParam;
int length = 1;
while (loopNode.next != loopNodeParam) {
length++;
loopNode = loopNode.next;
}
return length;
}
}

38
algorithms/src/main/java/com/baeldung/algorithms/linkedlist/CycleRemovalWithoutCountingLoopNodes.java Normal file
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package com.baeldung.algorithms.linkedlist;
public class CycleRemovalWithoutCountingLoopNodes {
public static <T> boolean detectAndRemoveCycle(Node<T> head) {
if (head == null) {
return false;
}
Node<T> slow = head;
Node<T> fast = head;
while (fast != null && fast.next != null) {
slow = slow.next;
fast = fast.next.next;
if (slow == fast) {
removeCycle(slow, head);
return true;
}
}
return false;
}
private static <T> void removeCycle(Node<T> meetingPointParam, Node<T> head) {
Node<T> loopNode = meetingPointParam;
Node<T> it = head;
while (loopNode.next != it.next) {
it = it.next;
loopNode = loopNode.next;
}
loopNode.next = null;
}
}

38
algorithms/src/main/java/com/baeldung/algorithms/linkedlist/Node.java Normal file
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package com.baeldung.algorithms.linkedlist;
public class Node<T> {
T data;
Node<T> next;
public static <T> Node<T> createNewNode(T data, Node<T> next) {
Node<T> node = new Node<T>();
node.data = data;
node.next = next;
return node;
}
public static <T> void traverseList(Node<T> root) {
if (root == null) {
return;
}
Node<T> node = root;
while (node != null) {
System.out.println(node.data);
node = node.next;
}
}
public static <T> Node<T> getTail(Node<T> root) {
if (root == null) {
return null;
}
Node<T> node = root;
while (node.next != null) {
node = node.next;
}
return node;
}
}

20
algorithms/src/test/java/com/baeldung/algorithms/linkedlist/CycleDetectionBruteForceTest.java Normal file
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package com.baeldung.algorithms.linkedlist;
import org.junit.Assert;
import org.junit.Test;
public class CycleDetectionBruteForceTest extends CycleDetectionTestBase {
@Test
public void givenNormalList_dontDetectLoop() {
Node<Integer> root = createList();
Assert.assertFalse(CycleDetectionBruteForce.detectCycle(root));
}
@Test
public void givenCyclicList_detectLoop() {
Node<Integer> root = createList();
createLoop(root);
Assert.assertTrue(CycleDetectionBruteForce.detectCycle(root));
}
}

20
algorithms/src/test/java/com/baeldung/algorithms/linkedlist/CycleDetectionByFastAndSlowIteratorsTest.java Normal file
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package com.baeldung.algorithms.linkedlist;
import org.junit.Assert;
import org.junit.Test;
public class CycleDetectionByFastAndSlowIteratorsTest extends CycleDetectionTestBase {
@Test
public void givenNormalList_dontDetectLoop() {
Node<Integer> root = createList();
Assert.assertFalse(CycleDetectionByFastAndSlowIterators.detectCycle(root));
}
@Test
public void givenCyclicList_detectLoop() {
Node<Integer> root = createList();
createLoop(root);
Assert.assertTrue(CycleDetectionByFastAndSlowIterators.detectCycle(root));
}
}

20
algorithms/src/test/java/com/baeldung/algorithms/linkedlist/CycleDetectionByHashingTest.java Normal file
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package com.baeldung.algorithms.linkedlist;
import org.junit.Assert;
import org.junit.Test;
public class CycleDetectionByHashingTest extends CycleDetectionTestBase {
@Test
public void givenNormalList_dontDetectLoop() {
Node<Integer> root = createList();
Assert.assertFalse(CycleDetectionByHashing.detectCycle(root));
}
@Test
public void givenCyclicList_detectLoop() {
Node<Integer> root = createList();
createLoop(root);
Assert.assertTrue(CycleDetectionByHashing.detectCycle(root));
}
}

27
algorithms/src/test/java/com/baeldung/algorithms/linkedlist/CycleDetectionTestBase.java Normal file
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package com.baeldung.algorithms.linkedlist;
public class CycleDetectionTestBase {
public static Node<Integer> createList() {
Node<Integer> root = Node.createNewNode(10, null);
for (int i = 9; i >= 1; --i) {
Node<Integer> current = Node.createNewNode(i, root);
root = current;
}
return root;
}
public static void createLoop(Node<Integer> root) {
Node<Integer> tail = Node.getTail(root);
Node<Integer> middle = root;
for (int i = 1; i <= 4; i++) {
middle = middle.next;
}
tail.next = middle;
}
}

21
algorithms/src/test/java/com/baeldung/algorithms/linkedlist/CycleRemovalBruteForceTest.java Normal file
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package com.baeldung.algorithms.linkedlist;
import org.junit.Assert;
import org.junit.Test;
public class CycleRemovalBruteForceTest extends CycleDetectionTestBase {
@Test
public void givenNormalList_dontDetectLoop() {
Node<Integer> root = createList();
Assert.assertFalse(CycleRemovalBruteForce.detectAndRemoveCycle(root));
}
@Test
public void givenCyclicList_detectAndRemoveLoop() {
Node<Integer> root = createList();
createLoop(root);
Assert.assertTrue(CycleRemovalBruteForce.detectAndRemoveCycle(root));
Assert.assertFalse(CycleDetectionByFastAndSlowIterators.detectCycle(root));
}
}

21
algorithms/src/test/java/com/baeldung/algorithms/linkedlist/CycleRemovalByCountingLoopNodesTest.java Normal file
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package com.baeldung.algorithms.linkedlist;
import org.junit.Assert;
import org.junit.Test;
public class CycleRemovalByCountingLoopNodesTest extends CycleDetectionTestBase {
@Test
public void givenNormalList_dontDetectLoop() {
Node<Integer> root = createList();
Assert.assertFalse(CycleRemovalByCountingLoopNodes.detectAndRemoveCycle(root));
}
@Test
public void givenCyclicList_detectAndRemoveLoop() {
Node<Integer> root = createList();
createLoop(root);
Assert.assertTrue(CycleRemovalByCountingLoopNodes.detectAndRemoveCycle(root));
Assert.assertFalse(CycleDetectionByFastAndSlowIterators.detectCycle(root));
}
}

21
algorithms/src/test/java/com/baeldung/algorithms/linkedlist/CycleRemovalWithoutCountingLoopNodesTest.java Normal file
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package com.baeldung.algorithms.linkedlist;
import org.junit.Assert;
import org.junit.Test;
public class CycleRemovalWithoutCountingLoopNodesTest extends CycleDetectionTestBase {
@Test
public void givenNormalList_dontDetectLoop() {
Node<Integer> root = createList();
Assert.assertFalse(CycleRemovalWithoutCountingLoopNodes.detectAndRemoveCycle(root));
}
@Test
public void givenCyclicList_detectAndRemoveLoop() {
Node<Integer> root = createList();
createLoop(root);
Assert.assertTrue(CycleRemovalWithoutCountingLoopNodes.detectAndRemoveCycle(root));
Assert.assertFalse(CycleDetectionByFastAndSlowIterators.detectCycle(root));
}
}