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+### https://theweeklychallenge.org/blog/perl-weekly-challenge-245/
+"""
+
+Task 2: Largest of Three
+
+Submitted by: [46]Mohammad S Anwar
+     __________________________________________________________________
+
+   You are given an array of integers >= 0.
+
+   Write a script to return the largest number formed by concatenating
+   some of the given integers in any order which is also multiple of 3.
+   Return -1 if none found.
+
+Example 1
+
+Input: @ints = (8, 1, 9)
+Output: 981
+
+981 % 3 == 0
+
+Example 2
+
+Input: @ints = (8, 6, 7, 1, 0)
+Output: 8760
+
+Example 3
+
+Input: @ints = (1)
+Output: -1
+     __________________________________________________________________
+
+   Last date to submit the solution 23:59 (UK Time) Sunday 3rd December
+   2023.
+     __________________________________________________________________
+
+SO WHAT DO YOU THINK ?
+"""
+### solution by pokgopun@gmail.com
+
+from itertools import permutations, chain
+
+def permutes(tup: tuple):
+    for n in range(1,len(tup)+1):   ### need permutations(tup,n) loop instead of permutations(tup) alone to avoid a bug in itertools/permutations
+        yield permutations(tup, n)
+
+def intsOfThree(tup: tuple):
+    for ints in chain.from_iterable(permutes(tup)):
+        if sum(ints) % 3 == 0:   ### If a + b = c , then a ( mod N ) + b ( mod N ) ≡ c ( mod N )
+            yield ints
+
+def intOfThree(tup: tuple):
+    for iStrs in  ((str(i) for i in ints) for ints in intsOfThree(tup)):   ### int-to-string conversion for ints so we can further concat and convert them to an int
+        yield int("".join(iStrs))   ### concat and convert int strings to an int
+
+def largestOfThree(tup: tuple):
+    return max(   ### max() can avoid an error from null permute iterator as it operates on chain.from_iterables that include default (-1,)
+            chain.from_iterable(
+                (
+                    intOfThree(tup),
+                    (-1,)   ### add (-1,) to chain.from_iterable to avoid max() error from null iterator from permutations (i.e. when nothing qualifies sum % 3 == 0
+                    )
+                )
+            )
+
+for inpt, otpt in {
+        (8, 1, 9): 981,
+        (8, 6, 7, 1, 0): 8760,
+        (1,): -1,
+        (0,0,0): 0,
+        (4, 8, 911): 9114,
+        (8, 85, 0): 8850,
+        (8, 89, 2): 8982,
+        (8, 76, 0): 8760,
+        (8, 94, 0): 9480,
+        }.items():
+    print(otpt==largestOfThree(inpt))