Diameter: node visits, naive vs one pass (counted, not timed)
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tree                      nodes   naive visits     one-pass   diameter
sample (9)                    9             26            9          7
perfect, 4 levels            15             49           15          7
perfect, 7 levels           127            769          127         13
perfect, 10 levels         1023           9217         1023         19
left-skewed 100             100           5050          100        100
left-skewed 1000           1000         500500         1000       1000
left-skewed 2000           2000        2001000         2000       2000