backtrack

Author: idf

301 Remove Invalid Parentheses.py

@@ -0,0 +1,71 @@
+"""
+Remove the minimum number of invalid parentheses in order to make the input string valid. Return all possible results.
+
+Note: The input string may contain letters other than the parentheses ( and ).
+
+Examples:
+"()())()" -> ["()()()", "(())()"]
+"(a)())()" -> ["(a)()()", "(a())()"]
+")(" -> [""]
+
+"""
+__author__ = 'Daniel'
+
+
+class Solution(object):
+    def removeInvalidParentheses(self, s):
+        """
+        :type s: str
+        :rtype: List[str]
+        """
+        n = len(s)
+        # solve min count of removal
+        cnt = 0
+        l = 0
+        for c in s:
+            if c == "(":
+                l += 1
+            elif c == ")":
+                l -= 1
+                if l < 0:
+                    l = 0
+                    cnt += 1
+
+        cnt += l
+        ret = []
+        self.dfs(s, "", 0, None, 0, cnt, ret)
+        return ret
+
+    def dfs(self, s, cur, l, removed, i, cnt, ret):
+        """backtracking, pre-check"""
+        if l < 0 or cnt < 0 or i > len(s):
+            return
+        if i == len(s):
+            if cnt == 0 and l == 0:
+                ret.append(cur)
+            return
+
+        if s[i] in ("(", ")"):
+            # jump
+            C = cnt
+            while i < len(s) and removed and removed == s[i]:
+                i += 1
+                C -= 1
+
+            if C != cnt:
+                self.dfs(s, cur, l, removed, i, C, ret)
+            else:
+                self.dfs(s, cur, l, s[i], i+1, cnt-1, ret)
+
+                L = l+1 if s[i] == "(" else l-1
+                self.dfs(s, cur+s[i], L, None, i+1, cnt, ret)  # put
+        else:
+            self.dfs(s, cur+s[i], l, None, i+1, cnt, ret)
+
+
+if __name__ == "__main__":
+    assert Solution().removeInvalidParentheses("(a)())()") == ['(a())()', '(a)()()']
+
+
+
+