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Author: hogan-tech

4020-lexicographically-smallest-permutation-greater-than-target/4020-lexicographically-smallest-permutation-greater-than-target.py

@@ -0,0 +1,51 @@
+# time complexity: O(n*n!)
+# space complexity: O(n)
+class Solution:
+    def lexGreaterPermutation(self, s: str, target: str) -> str:
+        n = len(s)
+        sCount = [0] * 26
+        for c in s:
+            sCount[ord(c) - ord('a')] += 1
+
+        result = None
+        def backtrack(i: int, prefix: str, count: list, greater: bool):
+            nonlocal result
+            if result is not None and prefix >= result:
+                return
+            if i == n:
+                if prefix > target:
+                    if result is None or prefix < result:
+                        result = prefix
+                return
+            for c in range(26):
+                if count[c] == 0:
+                    continue
+                currC = chr(c + ord('a'))
+                if not greater and currC < target[i]:
+                    continue
+                if not greater and currC == target[i]:
+                    count[c] -= 1
+                    backtrack(i + 1, prefix + currC, count, False)
+                    count[c] += 1
+                elif greater or currC > target[i]:
+                    count[c] -= 1
+                    backtrack(i + 1, prefix + currC, count, True)
+                    count[c] += 1
+
+        backtrack(0, "", sCount, False)
+        
+        if result:
+            return result
+        
+        return ""
+
+
+s = "abc"
+target = "bba"
+print(Solution().lexGreaterPermutation(s, target))
+s = "leet"
+target = "code"
+print(Solution().lexGreaterPermutation(s, target))
+s = "baba"
+target = "bbaa"
+print(Solution().lexGreaterPermutation(s, target))