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Problem 5 of 159Easy
LeetCode
LeetCodeConcatenation of Array
Arrays & Strings
Asked at 7 companies
6 recent
- Amazon
- Bloomberg
- Infosys
- Microsoft
- Meta
- GE Healthcare
Community-reported · source · updated 2026-10-08. ● asked in the last 6 months.
Go step by step: try it yourself before the video and the visual. Progress saves on this device.
Step 1
Know these before you start
Tick what you already know
Concept videoStep 2
Try it on paper
5–10 minutes, no code yet
About this problem
Read and write values in a list. Almost every interview pattern starts here.
Read the full statement and examples on LeetCode, try it for 20–30 minutes, then come back for the walkthrough and the step-by-step visual.
Step 6
Get it accepted
All test cases pass
Step 7
Review it so it sticks
Re-solve from memory after
Solve it yourself before you look
Reading the solution first feels like progress, but it makes the next similar problem — and the interview version — much harder, because you skipped the part where you figure it out. Give it an honest 20–30 minutes. Stuck? Re-read the pattern, watch the concept video, or try the brute force first.
Hidden: optimal solution