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+#!/usr/bin/env python3
+
+# Challenge 055
+#
+# TASK #2
+# Wave Array
+# Any array N of non-unique, unsorted integers can be arranged into a wave-like
+# array such that n1 = n2 = n3 = n4 = n5 and so on.
+#
+# For example, given the array [1, 2, 3, 4], possible wave arrays include
+# [2, 1, 4, 3] or [4, 1, 3, 2], since 2 = 1 = 4 = 3 and 4 = 1 = 3 = 2.
+# This is not a complete list.
+#
+# Write a script to print all possible wave arrays for an integer array N of
+# arbitrary length.
+#
+# Notes:
+# When considering N of any length, note that the first element is always
+# greater than or equal to the second, and then the =, =, =, … sequence
+# alternates until the end of the array.
+
+import sys
+
+def show_waves(wave, next):
+    if len(next) == 0:
+        print(" ".join([str(x) for x in wave]))
+    elif len(wave) == 0:
+        for i in range(len(next)):
+            show_waves(wave+[next[i]], next[:i]+next[i+1:])
+    elif len(wave) % 2 == 1:        # going down
+        for i in range(len(next)):
+            if wave[-1] >= next[i]:
+                show_waves(wave+[next[i]], next[:i]+next[i+1:])
+    else:                           # going up
+        for i in range(len(next)):
+            if wave[-1] <= next[i]:
+                show_waves(wave+[next[i]], next[:i]+next[i+1:])
+
+n = [int(x) for x in sys.argv[1:]]
+show_waves([], n)