package Others;

import java.util.Arrays;

/**
 * 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/
 */
class TwoPointers {

 public static void main(String[] args) {
 int[] arr = {10, 20, 35, 50, 75, 80};
 int key = 70;
 assert isPairedSum(arr, key); /* 20 + 60 == 70 */

 arr = new int[]{1, 2, 3, 4, 5, 6, 7};
 key = 13;
 assert isPairedSum(arr, key); /* 6 + 7 == 13 */

 key = 14;
 assert !isPairedSum(arr, key);
 }

 /**
 * Given a sorted array arr (sorted in ascending order).
 * Find if there exists any pair of elements such that their sum is equal to key.
 *
 * @param arr the array contains elements
 * @param key the number to search
 * @return {@code true} if there exists a pair of elements, {@code false} otherwise.
 */
 private static boolean isPairedSum(int[] arr, int key) {
 /* array sorting is necessary for this algorithm to function correctly */
 Arrays.sort(arr);
 int i = 0; /* index of first element */
 int j = arr.length - 1; /* index of last element */

 while (i < j) {
 if (arr[i] + arr[j] == key) {
 return true;
 } else if (arr[i] + arr[j] < key) {
 i++;
 } else {
 j--;
 }
 }
 return false;
 }
}