interview training: permutations

puzzles/interviews/training/permutation.py

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+#
+#   Prints all permutations.
+#
+def permutation(s, b, e):
+    if b+1 == e:
+        print(s)
+    else:
+        for i in range(b, e-1):
+            permutation(s, b+1, e)
+            c = s[i+1]
+            s[i+1] = s[i]
+            s[i] = s[b]
+            s[b] = c
+        permutation(s, b+1, e)
+        c = s[b]
+        s[b] = s[e-1]
+        s[e-1] = c
+
+#
+#   Prints all permutations. But in addition doesn't print
+#   multiple instances of same value.
+#   e.g. abb bab bba  ( doesn't print two abb )
+#
+def permutation2(s):
+    print(s)
+    l = len(s)
+
+    while True:
+        i = l-1
+        while True:
+            ii = i
+            i = i - 1
+            if ord(s[i]) < ord(s[ii]):
+                j = l-1
+                while ord(s[i]) >= ord(s[j]):
+                    j = j - 1
+                s[i], s[j] = s[j], s[i]
+                s[ii:l] = s[ii:l][::-1]
+                print(s)
+                break
+            if i == 0:
+                return
+
+if __name__ == "__main__":
+    s = ['a', 'b', 'c', 'd', 'e', 'e']
+    permutation(s, 0, len(s))
+    print("--------------------------------------------")
+    permutation2(s)