TwoSumProblem.java

package com.thealgorithms.misc;

import java.util.HashMap;
import java.util.Optional;
import org.apache.commons.lang3.tuple.Pair;

public final class TwoSumProblem {
 private TwoSumProblem() {
 }

 /**
 * The function "twoSum" takes an array of integers and a target integer as input, and returns an
 * array of two indices where the corresponding elements in the input array add up to the target.
 * @param values An array of integers.
 * @param target The target is the sum that we are trying to find using two numbers from the given array.
 * @return A pair or indexes such that sum of values at these indexes equals to the target
 * @author Bama Charan Chhandogi (https://github.com/BamaCharanChhandogi)
 */

 public static Optional<Pair<Integer, Integer>> twoSum(final int[] values, final int target) {
 HashMap<Integer, Integer> valueToIndex = new HashMap<>();
 for (int i = 0; i < values.length; i++) {
 final var remainder = target - values[i];
 if (valueToIndex.containsKey(remainder)) {
 return Optional.of(Pair.of(valueToIndex.get(remainder), i));
 }
 if (!valueToIndex.containsKey(values[i])) {
 valueToIndex.put(values[i], i);
 }
 }
 return Optional.empty();
 }
}