From cd3f0fcb1f1a4e782a470ad66da197be0a2aab1b Mon Sep 17 00:00:00 2001 From: Dhananjay Singh Date: Fri, 4 Jan 2019 05:10:26 +0530 Subject: [PATCH] BAEL-2391 Two pointer technique * two pointer technique * Corrected two sum * Changed asserts in unit test --- .../LinkedListFindMiddle.java | 16 ++++++ .../twopointertechnique/MyNode.java | 20 +++++++ .../twopointertechnique/RotateArray.java | 22 ++++++++ .../twopointertechnique/TwoSum.java | 38 +++++++++++++ .../LinkedListFindMiddleUnitTest.java | 37 ++++++++++++ .../RotateArrayUnitTest.java | 26 +++++++++ .../twopointertechnique/TwoSumUnitTest.java | 56 +++++++++++++++++++ 7 files changed, 215 insertions(+) create mode 100644 algorithms-miscellaneous-1/src/main/java/com/baeldung/algorithms/twopointertechnique/LinkedListFindMiddle.java create mode 100644 algorithms-miscellaneous-1/src/main/java/com/baeldung/algorithms/twopointertechnique/MyNode.java create mode 100644 algorithms-miscellaneous-1/src/main/java/com/baeldung/algorithms/twopointertechnique/RotateArray.java create mode 100644 algorithms-miscellaneous-1/src/main/java/com/baeldung/algorithms/twopointertechnique/TwoSum.java create mode 100644 algorithms-miscellaneous-1/src/test/java/com/baeldung/algorithms/twopointertechnique/LinkedListFindMiddleUnitTest.java create mode 100644 algorithms-miscellaneous-1/src/test/java/com/baeldung/algorithms/twopointertechnique/RotateArrayUnitTest.java create mode 100644 algorithms-miscellaneous-1/src/test/java/com/baeldung/algorithms/twopointertechnique/TwoSumUnitTest.java diff --git a/algorithms-miscellaneous-1/src/main/java/com/baeldung/algorithms/twopointertechnique/LinkedListFindMiddle.java b/algorithms-miscellaneous-1/src/main/java/com/baeldung/algorithms/twopointertechnique/LinkedListFindMiddle.java new file mode 100644 index 0000000000..a7031f4fba --- /dev/null +++ b/algorithms-miscellaneous-1/src/main/java/com/baeldung/algorithms/twopointertechnique/LinkedListFindMiddle.java @@ -0,0 +1,16 @@ +package com.baeldung.algorithms.twopointertechnique; + +public class LinkedListFindMiddle { + + public T findMiddle(MyNode head) { + MyNode slowPointer = head; + MyNode fastPointer = head; + + while (fastPointer.next != null && fastPointer.next.next != null) { + fastPointer = fastPointer.next.next; + slowPointer = slowPointer.next; + } + return slowPointer.data; + } + +} diff --git a/algorithms-miscellaneous-1/src/main/java/com/baeldung/algorithms/twopointertechnique/MyNode.java b/algorithms-miscellaneous-1/src/main/java/com/baeldung/algorithms/twopointertechnique/MyNode.java new file mode 100644 index 0000000000..7d93f03ef9 --- /dev/null +++ b/algorithms-miscellaneous-1/src/main/java/com/baeldung/algorithms/twopointertechnique/MyNode.java @@ -0,0 +1,20 @@ +package com.baeldung.algorithms.twopointertechnique; + +public class MyNode { + MyNode next; + E data; + + public MyNode(E value) { + data = value; + next = null; + } + + public MyNode(E value, MyNode n) { + data = value; + next = n; + } + + public void setNext(MyNode n) { + next = n; + } +} diff --git a/algorithms-miscellaneous-1/src/main/java/com/baeldung/algorithms/twopointertechnique/RotateArray.java b/algorithms-miscellaneous-1/src/main/java/com/baeldung/algorithms/twopointertechnique/RotateArray.java new file mode 100644 index 0000000000..b4e3698c01 --- /dev/null +++ b/algorithms-miscellaneous-1/src/main/java/com/baeldung/algorithms/twopointertechnique/RotateArray.java @@ -0,0 +1,22 @@ +package com.baeldung.algorithms.twopointertechnique; + +public class RotateArray { + + public void rotate(int[] input, int step) { + step %= input.length; + reverse(input, 0, input.length - 1); + reverse(input, 0, step - 1); + reverse(input, step, input.length - 1); + } + + private void reverse(int[] input, int start, int end) { + while (start < end) { + int temp = input[start]; + input[start] = input[end]; + input[end] = temp; + start++; + end--; + } + } + +} diff --git a/algorithms-miscellaneous-1/src/main/java/com/baeldung/algorithms/twopointertechnique/TwoSum.java b/algorithms-miscellaneous-1/src/main/java/com/baeldung/algorithms/twopointertechnique/TwoSum.java new file mode 100644 index 0000000000..14eceaa1bd --- /dev/null +++ b/algorithms-miscellaneous-1/src/main/java/com/baeldung/algorithms/twopointertechnique/TwoSum.java @@ -0,0 +1,38 @@ +package com.baeldung.algorithms.twopointertechnique; + +public class TwoSum { + + public boolean twoSum(int[] input, int targetValue) { + + int pointerOne = 0; + int pointerTwo = input.length - 1; + + while (pointerOne < pointerTwo) { + int sum = input[pointerOne] + input[pointerTwo]; + + if (sum == targetValue) { + return true; + } else if (sum < targetValue) { + pointerOne++; + } else { + pointerTwo--; + } + } + + return false; + } + + public boolean twoSumSlow(int[] input, int targetValue) { + + for (int i = 0; i < input.length; i++) { + for (int j = 1; j < input.length; j++) { + if (input[i] + input[j] == targetValue) { + return true; + } + } + } + + return false; + } + +} diff --git a/algorithms-miscellaneous-1/src/test/java/com/baeldung/algorithms/twopointertechnique/LinkedListFindMiddleUnitTest.java b/algorithms-miscellaneous-1/src/test/java/com/baeldung/algorithms/twopointertechnique/LinkedListFindMiddleUnitTest.java new file mode 100644 index 0000000000..422a53fa3e --- /dev/null +++ b/algorithms-miscellaneous-1/src/test/java/com/baeldung/algorithms/twopointertechnique/LinkedListFindMiddleUnitTest.java @@ -0,0 +1,37 @@ +package com.baeldung.algorithms.twopointertechnique; + +import static org.assertj.core.api.Assertions.assertThat; + +import org.junit.Test; + +public class LinkedListFindMiddleUnitTest { + + LinkedListFindMiddle linkedListFindMiddle = new LinkedListFindMiddle(); + + @Test + public void givenLinkedListOfMyNodes_whenLinkedListFindMiddle_thenCorrect() { + + MyNode head = createNodesList(8); + + assertThat(linkedListFindMiddle.findMiddle(head)).isEqualTo("4"); + + head = createNodesList(9); + + assertThat(linkedListFindMiddle.findMiddle(head)).isEqualTo("5"); + } + + private static MyNode createNodesList(int n) { + + MyNode head = new MyNode("1"); + MyNode current = head; + + for (int i = 2; i <= n; i++) { + MyNode newNode = new MyNode(String.valueOf(i)); + current.setNext(newNode); + current = newNode; + } + + return head; + } + +} diff --git a/algorithms-miscellaneous-1/src/test/java/com/baeldung/algorithms/twopointertechnique/RotateArrayUnitTest.java b/algorithms-miscellaneous-1/src/test/java/com/baeldung/algorithms/twopointertechnique/RotateArrayUnitTest.java new file mode 100644 index 0000000000..da227ae751 --- /dev/null +++ b/algorithms-miscellaneous-1/src/test/java/com/baeldung/algorithms/twopointertechnique/RotateArrayUnitTest.java @@ -0,0 +1,26 @@ +package com.baeldung.algorithms.twopointertechnique; + +import static org.assertj.core.api.Assertions.assertThat; + +import org.junit.Test; + +public class RotateArrayUnitTest { + + private RotateArray rotateArray = new RotateArray(); + + private int[] inputArray; + + private int step; + + @Test + public void givenAnArrayOfIntegers_whenRotateKsteps_thenCorrect() { + + inputArray = new int[] { 1, 2, 3, 4, 5, 6, 7 }; + step = 4; + + rotateArray.rotate(inputArray, step); + + assertThat(inputArray).containsExactly(new int[] { 4, 5, 6, 7, 1, 2, 3 }); + } + +} diff --git a/algorithms-miscellaneous-1/src/test/java/com/baeldung/algorithms/twopointertechnique/TwoSumUnitTest.java b/algorithms-miscellaneous-1/src/test/java/com/baeldung/algorithms/twopointertechnique/TwoSumUnitTest.java new file mode 100644 index 0000000000..aa76f8e1cf --- /dev/null +++ b/algorithms-miscellaneous-1/src/test/java/com/baeldung/algorithms/twopointertechnique/TwoSumUnitTest.java @@ -0,0 +1,56 @@ +package com.baeldung.algorithms.twopointertechnique; + +import static org.junit.Assert.assertFalse; +import static org.junit.Assert.assertTrue; + +import org.junit.Test; + +public class TwoSumUnitTest { + + private TwoSum twoSum = new TwoSum(); + + private int[] sortedArray; + + private int targetValue; + + @Test + public void givenASortedArrayOfIntegers_whenTwoSumSlow_thenPairExists() { + + sortedArray = new int[] { 0, 1, 2, 3, 4, 5, 5, 6, 7, 8, 9, 9 }; + + targetValue = 12; + + assertTrue(twoSum.twoSumSlow(sortedArray, targetValue)); + } + + @Test + public void givenASortedArrayOfIntegers_whenTwoSumSlow_thenPairDoesNotExists() { + + sortedArray = new int[] { 0, 1, 2, 3, 4, 5, 5, 6, 7, 8, 9, 9 }; + + targetValue = 20; + + assertFalse(twoSum.twoSumSlow(sortedArray, targetValue)); + } + + @Test + public void givenASortedArrayOfIntegers_whenTwoSum_thenPairExists() { + + sortedArray = new int[] { 0, 1, 2, 3, 4, 5, 5, 6, 7, 8, 9, 9 }; + + targetValue = 12; + + assertTrue(twoSum.twoSum(sortedArray, targetValue)); + } + + @Test + public void givenASortedArrayOfIntegers_whenTwoSum_thenPairDoesNotExists() { + + sortedArray = new int[] { 0, 1, 2, 3, 4, 5, 5, 6, 7, 8, 9, 9 }; + + targetValue = 20; + + assertFalse(twoSum.twoSum(sortedArray, targetValue)); + } + +}