June 2018 Update

Task/Find-the-missing-permutation/Julia/find-the-missing-permutation-1.julia

@@ -1,15 +1,13 @@
-function find_missing_permutations{T<:String}(a::Array{T,1})
-    std = unique(sort(split(a[1], "")))
-    needsperm = trues(factorial(length(std)))
-    for s in a
-        b = split(s, "")
-        p = map(x->findfirst(std, x), b)
-        isperm(p) || throw(DomainError())
-        needsperm[nthperm(p)] = false
+using Combinatorics
+function missingperm(arr::Vector)
+    allperms = permutations(arr[1])
+    for perm in allperms
+        perm = convert(eltype(arr), perm)
+        if perm ∉ arr return perm end
     end
-    mperms = T[]
-    for i in findn(needsperm)[1]
-        push!(mperms, join(nthperm(std, i), ""))
-    end
-    return mperms
 end
+
+arr = ["ABCD", "CABD", "ACDB", "DACB", "BCDA", "ACBD", "ADCB", "CDAB", "DABC", "BCAD",
+       "CADB", "CDBA", "CBAD", "ABDC", "ADBC", "BDCA", "DCBA", "BACD", "BADC", "BDAC",
+       "CBDA", "DBCA", "DCAB"]
+@show missingperm(arr)

Task/Find-the-missing-permutation/Julia/find-the-missing-permutation-2.julia

@@ -1,24 +1,17 @@
-test = ["ABCD", "CABD", "ACDB", "DACB", "BCDA", "ACBD",
-        "ADCB", "CDAB", "DABC", "BCAD", "CADB", "CDBA",
-        "CBAD", "ABDC", "ADBC", "BDCA", "DCBA", "BACD",
-        "BADC", "BDAC", "CBDA", "DBCA", "DCAB"]
-
-missperms = find_missing_permutations(test)
-
-print("The test list is:\n    ")
-i = 0
-for s in test
-    print(s, " ")
-    i += 1
-    i %= 5
-    i != 0 || print("\n    ")
-end
-i == 0 || println()
-if length(missperms) > 0
-    println("The following permutations are missing:")
-    for s in missperms
-        println("    ", s)
+function missingperm1(arr::Vector{<:AbstractString})
+    missperm = string()
+    for pos in 1:length(arr[1])
+        s = Set()
+        for perm in arr
+            c = perm[pos]
+            if c ∈ s pop!(s, c) else push!(s, c) end
+        end
+        missperm *= first(s)
     end
-else
-    println("There are no missing permutations.")
+    return missperm
 end
+
+using BenchmarkTools
+
+@btime missingperm(arr)
+@btime missingperm1(arr)