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Java Array Exercises: Find the sum of the two elements of a given array which is equal to a given integer

Java Array: Exercise-35 with Solution

Write a Java program to find the sum of the two elements of a given array which is equal to a given integer.
Sample array: [1,2,4,5,6]
Target value: 6.

Pictorial Presentation:

Java Array Exercises: Find the sum of the two elements of a given array which is equal to a given integer

Sample Solution:

Java Code:

import java.util.*;
public class Exercise35
{
        public static ArrayList<Integer> two_sum_array_target(final List<Integer> a, int b) {
        
        HashMap<Integer, Integer> my_map = new HashMap<Integer, Integer>();
        ArrayList<Integer> result = new ArrayList<Integer>();
        result.add(0);
        result.add(1);
        for(int i = 0; i < a.size(); i++){
            if(my_map.containsKey(a.get(i))){
                int index = my_map.get(a.get(i));
                result.set(0, index );
                result.set(1, i );
                break;
            }
            else{
                my_map.put(b - a.get(i), i);
            }
        }
        
        return result;
    }
  
    public static void main(String[] args){
        ArrayList<Integer> my_array = new ArrayList<Integer>();
        my_array.add(1);
        my_array.add(2);
        my_array.add(4);
        my_array.add(5);
		my_array.add(6);
		int target = 6;
        ArrayList<Integer> result = two_sum_array_target(my_array, target);
        for(int i : result)
            System.out.print("Index: "+i + " ");
    }
}

Sample Output:

                                                                              
Index: 1 Index: 2

Flowchart:

Flowchart: Java exercises: Find the sum of the two elements of a given array which is equal to a given integer

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Previous: Write a Java program to find the length of the longest consecutive elements sequence from a given unsorted array of integers.
Next: Write a Java program to find all the unique triplets such that sum of all the three elements [x, y, z (x ≤ y ≤ z)] equal to a specified number.

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Java: Tips of the Day

Array vs ArrayLists:

The main difference between these two is that an Array is of fixed size so once you have created an Array you cannot change it but the ArrayList is not of fixed size. You can create instances of ArrayLists without specifying its size. So if you create such instances of an ArrayList without specifying its size Java will create an instance of an ArrayList of default size.

Once an ArrayList is full it re-sizes itself. In fact, an ArrayList is internally supported by an array. So when an ArrayList is resized it will slow down its performance a bit as the contents of the old Array must be copied to a new Array.

At the same time, it's compulsory to specify the size of an Array directly or indirectly while creating it. And also Arrays can store both primitives and objects while ArrayLists only can store objects.

Ref: https://bit.ly/3o8L2KH