Based on 8 reported problems, Spotify interviews are in line with industry averages - 13% Hard vs 18% overall.
Compared to the industry average, Spotify puts unusual emphasis on heap-priority-queue (25% of problems, 4.1x the industry average), string (50% of problems, 1.8x the industry average), two-pointers (25% of problems, 1.8x the industry average). If you're short on time, these are the categories to double down on.
The most common topics are string (50%), array (25%), hash-table (25%), sorting (25%). Problems below are sorted by frequency, the ones at the top are asked most often.