The implementation uses two stacks internally with a slight optimization for space-constrainted situations.
First stack is where our actual values are kept, second is where we track the maximum value that currently lives in our first stack.
The max-stack is only appended to if the top of the max-stack is smaller than the value to be appended. It's also popped from only if the value being popped from the main stack is equal to the current maximum value.
This guarantees the max-stack doesn't grow with an O(n) rate, even on duplicate stack values.
find-max in this case is an O(1) since it peeks the top of the max-stack which will always contain the maximum value on the main stack, which gets updated every push/pop conditionally.
$ ruby -Itest test/max_test.rb
$ ruby -Itest test/mean_test.rbThere's a naive implementation of Max embedded in the benchmark executable script
$ bundle
$ bin/benchmark- Ruby 2.0, 2.2, 2.3
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