* Link: https://www.geeksforgeeks.org/two-pointers-technique/ */ -final class TwoPointers { +public final class TwoPointers { + private TwoPointers() { } /** - * Given a sorted array arr (sorted in ascending order), find if there exists - * any pair of elements such that their sum is equal to the key. + * Checks whether there exists a pair of elements in a sorted array whose sum equals the specified key. * - * @param arr the array containing elements (must be sorted in ascending order) - * @param key the number to search - * @return {@code true} if there exists a pair of elements, {@code false} otherwise. + * @param arr a sorted array of integers in ascending order (must not be null) + * @param key the target sum to find + * @return {@code true} if there exists at least one pair whose sum equals {@code key}, {@code false} otherwise + * @throws IllegalArgumentException if {@code arr} is {@code null} */ public static boolean isPairedSum(int[] arr, int key) { - int i = 0; // index of the first element - int j = arr.length - 1; // index of the last element + if (arr == null) { + throw new IllegalArgumentException("Input array must not be null."); + } + + int left = 0; + int right = arr.length - 1; + + while (left < right) { + int sum = arr[left] + arr[right]; - while (i < j) { - int sum = arr[i] + arr[j]; if (sum == key) { return true; - } else if (sum < key) { - i++; + } + if (sum < key) { + left++; } else { - j--; + right--; } } return false; diff --git a/src/test/java/com/thealgorithms/others/TwoPointersTest.java b/src/test/java/com/thealgorithms/others/TwoPointersTest.java index 3a174e0cd19e..6e0d2b22d280 100644 --- a/src/test/java/com/thealgorithms/others/TwoPointersTest.java +++ b/src/test/java/com/thealgorithms/others/TwoPointersTest.java @@ -1,6 +1,8 @@ package com.thealgorithms.others; +import static org.junit.jupiter.api.Assertions.assertEquals; import static org.junit.jupiter.api.Assertions.assertFalse; +import static org.junit.jupiter.api.Assertions.assertThrows; import static org.junit.jupiter.api.Assertions.assertTrue; import org.junit.jupiter.api.Test; @@ -69,4 +71,10 @@ void testPairExistsAtEdges() { int key = 9; assertTrue(TwoPointers.isPairedSum(arr, key)); } + + @Test + void isPairedSumShouldThrowExceptionWhenArrayIsNull() { + IllegalArgumentException exception = assertThrows(IllegalArgumentException.class, () -> TwoPointers.isPairedSum(null, 10)); + assertEquals("Input array must not be null.", exception.getMessage()); + } }
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