Data commit

Task/Permutations-by-swapping/Python/permutations-by-swapping-1.py

@@ -0,0 +1,60 @@
+from operator import itemgetter
+
+DEBUG = False # like the built-in __debug__
+
+def spermutations(n):
+    """permutations by swapping. Yields: perm, sign"""
+    sign = 1
+    p = [[i, 0 if i == 0 else -1] # [num, direction]
+         for i in range(n)]
+
+    if DEBUG: print ' #', p
+    yield tuple(pp[0] for pp in p), sign
+
+    while any(pp[1] for pp in p): # moving
+        i1, (n1, d1) = max(((i, pp) for i, pp in enumerate(p) if pp[1]),
+                           key=itemgetter(1))
+        sign *= -1
+        if d1 == -1:
+            # Swap down
+            i2 = i1 - 1
+            p[i1], p[i2] = p[i2], p[i1]
+            # If this causes the chosen element to reach the First or last
+            # position within the permutation, or if the next element in the
+            # same direction is larger than the chosen element:
+            if i2 == 0 or p[i2 - 1][0] > n1:
+                # The direction of the chosen element is set to zero
+                p[i2][1] = 0
+        elif d1 == 1:
+            # Swap up
+            i2 = i1 + 1
+            p[i1], p[i2] = p[i2], p[i1]
+            # If this causes the chosen element to reach the first or Last
+            # position within the permutation, or if the next element in the
+            # same direction is larger than the chosen element:
+            if i2 == n - 1 or p[i2 + 1][0] > n1:
+                # The direction of the chosen element is set to zero
+                p[i2][1] = 0
+        if DEBUG: print ' #', p
+        yield tuple(pp[0] for pp in p), sign
+
+        for i3, pp in enumerate(p):
+            n3, d3 = pp
+            if n3 > n1:
+                pp[1] = 1 if i3 < i2 else -1
+                if DEBUG: print ' # Set Moving'
+
+
+if __name__ == '__main__':
+    from itertools import permutations
+
+    for n in (3, 4):
+        print '\nPermutations and sign of %i items' % n
+        sp = set()
+        for i in spermutations(n):
+            sp.add(i[0])
+            print('Perm: %r Sign: %2i' % i)
+            #if DEBUG: raw_input('?')
+        # Test
+        p = set(permutations(range(n)))
+        assert sp == p, 'Two methods of generating permutations do not agree'

Task/Permutations-by-swapping/Python/permutations-by-swapping-2.py

@@ -0,0 +1,19 @@
+def s_permutations(seq):
+    def s_perm(seq):
+        if not seq:
+            return [[]]
+        else:
+            new_items = []
+            for i, item in enumerate(s_perm(seq[:-1])):
+                if i % 2:
+                    # step up
+                    new_items += [item[:i] + seq[-1:] + item[i:]
+                                  for i in range(len(item) + 1)]
+                else:
+                    # step down
+                    new_items += [item[:i] + seq[-1:] + item[i:]
+                                  for i in range(len(item), -1, -1)]
+            return new_items
+
+    return [(tuple(item), -1 if i % 2 else 1)
+            for i, item in enumerate(s_perm(seq))]

Task/Permutations-by-swapping/Python/permutations-by-swapping-3.py

@@ -0,0 +1,17 @@
+def s_permutations(seq):
+    items = [[]]
+    for j in seq:
+        new_items = []
+        for i, item in enumerate(items):
+            if i % 2:
+                # step up
+                new_items += [item[:i] + [j] + item[i:]
+                              for i in range(len(item) + 1)]
+            else:
+                # step down
+                new_items += [item[:i] + [j] + item[i:]
+                              for i in range(len(item), -1, -1)]
+        items = new_items
+
+    return [(tuple(item), -1 if i % 2 else 1)
+            for i, item in enumerate(items)]