Problem 024

git-svn-id: file:///srv/svn/euler@56 e5f4c3ec-3c0c-11df-b522-21efaa4426b5

e024.py

@@ -0,0 +1,29 @@
+import math
+
+def lexicographic_permutation(list, position):
+    items = len(list)
+    list = sorted(list)
+    p = []
+    position = position - 1
+    while len(p) < items:
+        index = 0 
+        # Find the next index to pop
+        l = len(list) - 1
+        f = math.factorial(l) if l else 0
+        while position and position >= f:
+            position = position - f
+            index = index + 1
+
+        p.append(list.pop(index))
+    return p
+
+if __name__ == '__main__':
+    print 'Testing permutations of 0..2:'
+    list = [str(i) for i in [0, 1, 2]]
+    for i in range(1, math.factorial(len(list)) + 1):
+        p = lexicographic_permutation(list, i)
+        print '\tPermutation', i, ''.join(p)
+
+    list = [str(i) for i in [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]]
+    p = lexicographic_permutation(list, 1000000)
+    print '1 millionth lexicographic permutation of 0..9:', ''.join(p)