{"input":[[1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,1]],"expected":true,"label":"Duplicate 1 at end, n=21"}
{"input":[[2147483647,-2147483648,0,2147483647]],"expected":true,"label":"Max-int duplicate"}
{"input":[[1,2,3,4,5,6,7,8,9,10]],"expected":false,"label":"All unique n=10 → false"}
