Counter arithmetic

Question

Counter arithmetic

Accepted Answer

Adding two Counters sums the counts for each key. 'a' appears 2 times in 'aab' and 1 time in 'abc', so a + b gives 'a': 3. 'b' appears once in each, giving 'b': 2. 'c' only appears in b with count 1. Counter also supports subtraction, intersection (&), and union (|), making it useful for bag/multiset arithmetic.