35 multiple-choice questions in College Board exam style. Each has four choices and a full explanation of why each option is right or wrong.
Mind the bounds: array indices are 0 to length−1; array uses .length, ArrayList uses .size().
Trace traversals element by element: especially removals from an ArrayList.
Binary search needs sorted data; recursion needs a reachable base case.
Read the explanations even when you got it right, and for 2D arrays remember rows = matrix.length, cols = matrix[0].length.