921. Minimum Add to Make Parentheses Valid

#method 1
class Solution:
    def minAddToMakeValid(self, s: str) -> int:
        ans=0
        op,cl=0,0
        for i in s:
            if i=='(':
                op+=1
            else:
                cl+=1
            if op<cl:
                ans+=1
                cl-=1
        ans+=abs(cl-op)
        return ans
#method 2
class Solution:
    def minAddToMakeValid(self, s: str) -> int:
        st=[]
        for i in s:
            if i=='(':
                st.append(i)
            else:
                if st and st[-1]=='(':
                    st.pop()
                else:
                    st.append(i)
        return len(st)