Two sum in Java
Java interview exercise on Algorithms & recursion, difficulty 2 of 3. Solve it in the editor beside a worked example, or cold in Interview mode with the example hidden; the tests run the moment you do.
Write twoSum(nums, target) that returns the indexes {i, j} (i < j) of the first pair whose values add up to target, scanning left to right with a HashMap from value to index, or an empty array when there is none. One pass: for each number, look up its complement before storing it.
Each exercise pairs a worked example with a twin problem to solve in a real editor; the tests run the moment you do. Interview mode hides the example: solve it from memory, without the hint or the solution, and it counts as solved cold. Progress is saved in your browser, and in your account if you sign in.