optimize allunique() for sorted collections (#50372)

base/set.jl

@@ -446,6 +446,8 @@ end
 
 Return `true` if all values from `itr` are distinct when compared with [`isequal`](@ref).
 
+`allunique` may use a specialized implementation when the input is sorted.
+
 See also: [`unique`](@ref), [`issorted`](@ref), [`allequal`](@ref).
 
 # Examples
@@ -494,7 +496,31 @@ allunique(::Union{AbstractSet,AbstractDict}) = true
 
 allunique(r::AbstractRange) = !iszero(step(r)) || length(r) <= 1
 
-allunique(A::StridedArray) = length(A) < 32 ? _indexed_allunique(A) : _hashed_allunique(A)
+function allunique(A::StridedArray)
+ if length(A) < 32
+ _indexed_allunique(A)
+ elseif OrderStyle(eltype(A)) === Ordered()
+ a1, rest1 = Iterators.peel(A)
+ a2, rest = Iterators.peel(rest1)
+ if !isequal(a1, a2)
+ compare = isless(a1, a2) ? isless : (a,b) -> isless(b,a)
+ for a in rest
+ if compare(a2, a)
+ a2 = a
+ elseif isequal(a2, a)
+ return false
+ else
+ return _hashed_allunique(A)
+ end
+ end
+ else # isequal(a1, a2)
+ return false
+ end
+ return true
+ else
+ _hashed_allunique(A)
+ end
+end
 
 function _indexed_allunique(A)
  length(A) < 2 && return true

test/sets.jl

@@ -580,6 +580,9 @@ end
  @test !allunique([1,1,2])
  @test !allunique([:a,:b,:c,:a])
  @test allunique(unique(randn(100))) # longer than 32
+ @test allunique(collect(1:100)) # sorted/unique && longer than 32
+ @test allunique(collect(100:-1:1)) # sorted/unique && longer than 32
+ @test !allunique(fill(1,100)) # sorted/repeating && longer than 32
  @test allunique(collect('A':'z')) # 58-element Vector{Char}
  @test !allunique(repeat(1:99, 1, 2))
  @test !allunique(vcat(pi, randn(1998), pi)) # longer than 1000