Free tool
Practice coding problems in your browser
Write a solution in a real editor and run it against the test cases without leaving the page. Your code runs in a sandbox inside your browser, so nothing is uploaded and nothing runs on a server. Pick a problem, write the function, and run the tests to see exactly which cases pass and which fail.
Two Sum
Given an array of integers `nums` and an integer `target`, return the indices of the two numbers that add up to `target`. Each input has exactly one solution; return the indices in ascending order.
Visible test cases
- twoSum([2,7,11,15], 9) == [0,1]
- twoSum([3,2,4], 6) == [1,2]
- twoSum([3,3], 6) == [0,1]
How the runner works
The editor calls the function you write with each test case's inputs and compares the return value to the expected output. Execution happens in a quickjs sandbox with a time limit, so an infinite loop or a heavy computation stops safely instead of freezing the page. These are visible practice cases meant for learning, not a graded submission, so you can experiment freely.