Python Program to Merge Two Arrays

You can merge two arrays in Python by using the + operator like merged = array1 + array2 or by using array1.extend(array2) to add elements of the second array to the first.

Examples

Input[1, 2, 3], [4, 5, 6]

Output[1, 2, 3, 4, 5, 6]

Input[], [7, 8]

Output[7, 8]

Input[10], []

Output[10]

How to Think About It

To merge two arrays, think of putting all elements from the second array right after the first array's elements. You can do this by creating a new array that contains all elements from both arrays or by adding the second array's elements directly to the first one.

Algorithm

1

Get the first array.

2

Get the second array.

3

Combine the two arrays by adding the second array's elements to the first.

4

Return or print the merged array.

Code

python

array1 = [1, 2, 3]
array2 = [4, 5, 6]
merged = array1 + array2
print(merged)

Output

[1, 2, 3, 4, 5, 6]

Dry Run

Let's trace merging [1, 2, 3] and [4, 5, 6] using the + operator.

1

Start with two arrays

array1 = [1, 2, 3], array2 = [4, 5, 6]

2

Add arrays using +

merged = array1 + array2 results in [1, 2, 3, 4, 5, 6]

3

Print merged array

Output: [1, 2, 3, 4, 5, 6]

Operation
merged = [1, 2, 3] + [4, 5, 6]
merged = [1, 2, 3, 4, 5, 6]

Why This Works

Step 1: Using + operator

The + operator creates a new array by joining elements of both arrays in order.

Step 2: Using extend() method

The extend() method adds elements of the second array to the end of the first array, modifying it in place.

Alternative Approaches

Using extend() method

python

array1 = [1, 2, 3]
array2 = [4, 5, 6]
array1.extend(array2)
print(array1)

This modifies the first array directly instead of creating a new one.

Using unpacking operator

python

array1 = [1, 2, 3]
array2 = [4, 5, 6]
merged = [*array1, *array2]
print(merged)

This creates a new array by unpacking elements from both arrays, useful for readability.

Complexity: O(n + m) time, O(n + m) space

Time Complexity

Merging requires visiting each element of both arrays once, so time grows with the total number of elements.

Space Complexity

Using + or unpacking creates a new array needing space for all elements; extend() modifies in place, saving space.

Which Approach is Fastest?

extend() is faster and uses less memory since it modifies the first array without creating a new one.

Approach	Time	Space	Best For
Using + operator	O(n + m)	O(n + m)	When you want a new merged array
Using extend()	O(m)	O(1)	When you want to add to the first array directly
Using unpacking	O(n + m)	O(n + m)	Readable new array creation