Create increasing-decreasing-string.py

Author: kamyu104

Python/increasing-decreasing-string.py

@@ -0,0 +1,47 @@
+# Time:  O(n)
+# Space: O(1)
+
+class Solution(object):
+    def sortString(self, s):
+        """
+        :type s: str
+        :rtype: str
+        """
+        result, count = [], [0]*26
+        for c in s:
+            count[ord(c)-ord('a')] += 1
+        while len(result) != len(s):
+            for c in xrange(len(count)):
+                if not count[c]:
+                    continue
+                result.append(chr(ord('a')+c))
+                count[c] -= 1
+            for c in reversed(xrange(len(count))):
+                if not count[c]:
+                    continue
+                result.append(chr(ord('a')+c))
+                count[c] -= 1
+        return "".join(result)
+
+
+# Time:  O(n)
+# Space: O(1)
+import collections
+
+
+class Solution2(object):
+    def sortString(self, s):
+        """
+        :type s: str
+        :rtype: str
+        """
+        result, count, desc = [], collections.Counter(s), False
+        while count:
+            for c in sorted(count.keys(), reverse=desc):
+                result.append(c)
+                count[c] -= 1
+                if not count[c]:
+                    del count[c]
+            desc = not desc
+        return "".join(result)
+