RosettaCodeData/Task/Find-the-missing-permutation/Run-BASIC/find-the-missing-permutatio...

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list$ = "ABCD CABD ACDB DACB BCDA ACBD ADCB CDAB DABC BCAD CADB CDBA CBAD ABDC ADBC BDCA DCBA BACD BADC BDAC CBDA DBCA DCAB"
for a = asc("A") to asc("D")
for b = asc("A") to asc("D")
for c = asc("A") to asc("D")
for d = asc("A") to asc("D")
x$ = chr$(a) + chr$(b) + chr$(c)+ chr$(d)
for i = 1 to 4 ' make sure each letter is unique
j = instr(x$,mid$(x$,i,1))
if instr(x$,mid$(x$,i,1),j + 1) <> 0 then goto [nxt]
next i
if instr(list$,x$) = 0 then print x$;" missing" ' found missing permutation
[nxt] next d
next c
next b
next a