Flatten Nested Array

Medium~15 min

Given a 2D array (an array of arrays of numbers), flatten it into a single 1D array.

The input is only one level deep — each element of the outer array is itself an array of numbers. Concatenate all the inner arrays in order to produce the result.

Examples

Example 1

Input: arr = [[1, 2], [3, 4], [5, 6]]

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

Explanation: The three inner arrays are concatenated in order.

Example 2

Input: arr = [[1], [2, 3, 4], [5]]

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

Explanation: Inner arrays can be different lengths.

Example 3

Input: arr = [[], [1, 2], []]

Output: [1, 2]

Explanation: Empty inner arrays contribute nothing to the result.

Constraints

0 <= arr.length <= 10^3
0 <= arr[i].length <= 10^3
-10^6 <= arr[i][j] <= 10^6
Total elements across all inner arrays <= 10^5

Code

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Output

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