added LEXF solution

LEXF.py

@@ -0,0 +1,48 @@
+#!/usr/bin/python
+
+#LEXF Rosalind.info Solution - Enumerating k-mers Lexicographically
+#Author: Peter Vlasveld
+#Date: 12/01/2019
+
+#get dataset from file
+f1 = open("rosalind_lexf.txt")
+content = f1.readlines()
+f1.close()
+
+#duplicate the lex set r times
+firstLex = content[0].split( )
+lex = []
+for i in xrange(0, int(content[1])):
+    lex.extend(firstLex)
+
+#recursive function to get all possible combinations within the lex set
+def wordCombo (arr, data, start, end, index, r):
+    if index == r:
+        tempStr = ""
+        for i in data:
+            tempStr += i
+        global comboList
+        comboList.append(tempStr)
+        return
+    i = start
+    while i <= end and end - i + 1 >= r - index:
+        data[index] = arr[i]
+        wordCombo(arr, data, i + 1, end, index + 1, r)
+        i += 1
+
+#empty lsit to be passed into function
+data = [0]*int(content[1])
+
+#global list to be filled with combinations
+comboList = []
+
+#run the function, remove duplicates, and sort it alhphabetically
+wordCombo(lex,data,0,len(lex)-1,0,int(content[1]))
+finalList = list(set(comboList))
+sortedList = sorted(finalList)
+
+#print the list to a file
+f2 = open("output.txt", "w")
+for i in sortedList:
+    f2.writelines(i + "\n")
+f2.close()