Count all pairs of numbers from a list where the ending digit of the ith number equals the starting digit of the jth number. Example [122, 21, 21, 23] should have 5 pairs (122, 21), (122, 21), (122, 23), (21, 122), (21, 122) - Approached it by taking least significant (%10) digit of the ith number and most significant digit (using log base 10 to compute successive division number by 10) of the jth number, but here the interviewer mentioned that log 122 is 22 (not sure how)