TwoSum.java

import org.junit.Assert;
 
/**
 * My solution of classical two sum problem in Java. 
  Problem - Given an array of
 * integers, find two numbers such that they add up to 
  a specific target number.
 *
 * The method twoSum should return indices of the two numbers such that they add
 * up to the target, where index1 must be less than index2. 
  Please note that
 * your returned answers (both index1 and index2) are not zero-based.
 *
 * Note: You may assume that each input would have exactly one solution.
 *
 * Example [2,7,11,15], 9 -> [1,2]
 * 
 * @author Javin Paul
 *
 */
public class TwoSum {
 
  public static int[] twoSum(int[] input, int target) {
    for (int i = 0; i < input.length; i++) {
 
      int first = input[i];
 
      for (int j = i + 1; j < input.length; j++) {
        int second = input[j];
        int total = first + second;
 
        if (total == target) {
          return new int[] { i + 1, j + 1 };
        }
      }
 
    }
    return null;
  }
 
  public static void main(String args[]) {
 
    // return pairs which adds to 29 in given array
    Assert.assertArrayEquals(new int[] { 1, 2 },  
          twoSum(new int[] { 12, 17, 21, 25 }, 29));
  }
}

Full solution - https://www.java67.com/2020/07/how-to-solve-two-sum-array-problem-in-java.html

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