First interviewer tested me on basic probability (Bayes rule etc), binary classification (saw if I knew precision/recall under a heavily unbalanced prior), and signal processing (sampling, aliasing). The coding part was to generate all ordered substrings of a given string. The 2nd interview was a basic test on probability followed by a coding problem (implement linked list, append operation, do in place reversal of list using a single walk through the list). Problems on the final interview were coding problems and basic number theory (implement binary search, implement FIR convolution, estimate frequency of a sine wave signal based on zero crossings, implement divisibility tests for various primes).
