further performance improvement

still room for optimisations; making deep copy because iterator is not
modifiable in for loops

src/vigenere/break_vig.py

@@ -17,6 +17,21 @@ def probe(key, substrings, words):
     return {key: val for key, val in key_hits.items() if val == best_val}
 
 
+def remove_crap_from_list(tree, max_depth, thr):
+    best = [-x * thr for x in range(max_depth+2)]
+    for key, val in tree.items():
+        if val > best[len(key)]:
+            best[len(key)] = val
+
+    import copy
+    tmp = copy.copy(list(tree.items()))
+    for key, val in tmp:
+        for i in range(len(key), max_depth+1):
+            if val < (best[i] - thr + (i-len(key))*thr*1.5):
+                del tree[key]
+                break
+
+
 def crack(substrings, words):
     tree = {"": 0}
     while tree:
@@ -26,6 +41,7 @@ def crack(substrings, words):
             return curr
         del tree[curr]
         tree.update(probe(curr, substrings, words))
+        remove_crap_from_list(tree, len(substrings[0]), 10)
 
 
 if __name__ == "__main__":