1047. Remove All Adjacent Duplicates In String

class Solution:
    def removeDuplicates(self, s: str) -> str:
       
        def solu1(s):
            """  tc O(N) sc  O(N)
            main idea: stack 

            """
            st = []
            for c in s:
                if st and st[-1] == c :
                    st.pop()
                else:
                    st.append(c)
            return ''.join(st)

        def solu2(s):
            """ tc O(N) sc O(1)
            @i: hold index set for next char in output 
            @cur: index of current iteration in the input string  
            """
            s  = list(s)
            i,n = 0, len(s)
            for cur in range(n):
                s[i] = s[cur]
                if i > 0 and s[i-1] == s[i]:  #duplicates = 2,can extend to k
                    i -= 2 
                i += 1 
            return ''.join(s[:i])