Create next-palindrome-using-same-digits.py

Author: kamyu104

Python/next-palindrome-using-same-digits.py

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+# Time:  O(n)
+# Space: O(1)
+
+class Solution(object):
+    def nextPalindrome(self, num):
+        """
+        :type num: str
+        :rtype: str
+        """
+        def next_permutation(nums, begin, end):
+            def reverse(nums, begin, end):
+                left, right = begin, end-1
+                while left < right:
+                    nums[left], nums[right] = nums[right], nums[left]
+                    left += 1
+                    right -= 1
+
+            k, l = begin-1, begin
+            for i in reversed(xrange(begin, end-1)):
+                if nums[i] < nums[i+1]:
+                    k = i
+                    break
+            else:
+                reverse(nums, begin, end)
+                return False
+            for i in reversed(xrange(k+1, end)):
+                if nums[i] > nums[k]:
+                    l = i
+                    break
+            nums[k], nums[l] = nums[l], nums[k]
+            reverse(nums, k+1, end)
+            return True
+        
+        nums = list(num)
+        if not next_permutation(nums, 0, len(nums)//2):
+            return ""
+        for i in xrange(len(nums)//2):
+            nums[-1-i] = nums[i]
+        return "".join(nums)