Minimum Remove to Make Valid Parentheses

class Solution:
    def minRemoveToMakeValid(self, s: str) -> str:
        sol = []
        lis = list(s)
        for i in range(len(s)):
            if lis[i] == "(":
                sol.append(i)
            elif lis[i] == ")":
                if len(sol) != 0:
                    sol.pop()
                else:
                    lis[i] = ""
        for i in sol:
            lis[i]=""
        return "".join(lis)