Can you sit the DSA for Frontend Certification today?

[10, 1, 21, 2].sort() with NO comparator produces what, and why?

• A[1, 10, 2, 21], because sort() without a comparator converts elements to STRINGS and compares lexicographically — '10' sorts before '2' as a string
• B[1, 2, 10, 21], sorted numerically by default
• CThe array is left unchanged
• DIt throws a TypeError

A function builds a new object for every element of an n-length array, each object holding one extra field alongside the original value. What is its auxiliary space complexity, and is it likely to cost more or less in practice than an equivalent function that maps to plain numbers?

• AO(n) either way in Big-O terms, but the object-per-element version typically costs more real memory per element (more bytes, more GC pressure) — a constant-factor difference Big-O doesn't capture
• BO(n²) for the object version, because objects are quadratically more expensive than numbers
• CO(1), because object creation doesn't count as space
• DO(log n), because objects are stored in a balanced structure internally

Why can iterating forward through an array with a normal for loop while calling arr.splice(i, 1) on matches produce incorrect results?

• Asplice() always throws an exception when called inside a loop
• Bsplice() only works on sorted arrays
• CRemoving an element shifts every later element's index down by one, so the loop's next index skips over the element that just slid into the removed position
• DThere is no issue — this pattern is always safe

Finding the single most frequent value by first building a frequency map, then scanning the map for the maximum count, has what overall complexity?

• AO(n), because two sequential linear passes (2n total operations) still simplify to O(n) — Big-O drops the constant factor
• BO(n²), because it scans twice, and Big-O multiplies sequential passes
• CO(n log n)
• DO(1)

A debounced search-as-you-type buffer that keeps extending while keystrokes arrive, and only resolves once typing pauses, most closely resembles which sliding-window shape?

• AA variable-size window whose right edge extends on every new event, and whose left edge (or resolution point) only 'closes' once the extending condition (new keystrokes arriving) stops
• BA fixed-size window with a constant, pre-determined size
• CTwo pointers moving in opposite directions toward each other
• DA window that never resolves once started