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Task/Best-shuffle/Python/best-shuffle-2.py

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+#!/usr/bin/env python
+
+def best_shuffle(s):
+    # Count the supply of characters.
+    from collections import defaultdict
+    count = defaultdict(int)
+    for c in s:
+        count[c] += 1
+
+    # Shuffle the characters.
+    r = []
+    for x in s:
+        # Find the best character to replace x.
+        best = None
+        rankb = -2
+        for c, rankc in count.items():
+            # Prefer characters with more supply.
+            # (Save characters with less supply.)
+            # Avoid identical characters.
+            if c == x: rankc = -1
+            if rankc > rankb:
+                best = c
+                rankb = rankc
+
+        # Add character to list. Remove it from supply.
+        r.append(best)
+        count[best] -= 1
+        if count[best] == 0: del count[best]
+
+    # If the final letter became stuck (as "ababcd" became "bacabd",
+    # and the final "d" became stuck), then fix it.
+    i = len(s) - 1
+    if r[i] == s[i]:
+        for j in range(i):
+            if r[i] != s[j] and r[j] != s[i]:
+                r[i], r[j] = r[j], r[i]
+                break
+
+    # Convert list to string. PEP 8, "Style Guide for Python Code",
+    # suggests that ''.join() is faster than + when concatenating
+    # many strings. See http://www.python.org/dev/peps/pep-0008/
+    r = ''.join(r)
+
+    score = sum(x == y for x, y in zip(r, s))
+
+    return (r, score)
+
+for s in "abracadabra", "seesaw", "elk", "grrrrrr", "up", "a":
+    shuffled, score = best_shuffle(s)
+    print("%s, %s, (%d)" % (s, shuffled, score))