TwoPointers.java

package com.thealgorithms.others;

/**
 * The two-pointer technique is a useful tool to utilize when searching for
 * pairs in a sorted array.
 *
 * <p>
 * Link: https://www.geeksforgeeks.org/two-pointers-technique/
 */
public final class TwoPointers {

 private TwoPointers() {
 }

 /**
 * Checks whether there exists a pair of elements in a sorted array whose sum equals the specified key.
 *
 * @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) {
 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];

 if (sum == key) {
 return true;
 }
 if (sum < key) {
 left++;
 } else {
 right--;
 }
 }
 return false;
 }
}