942. DI String Match

class Solution:
    def diStringMatch(self, S):
        string = collections.deque(range(len(S)+1))
        if S[0] == "I":
            flag = True  # True for from left to right, False for from right to left
            ans = [string.popleft()]
        else:
            flag = False
            ans = [string.pop()]
        for i in range(1, len(S)):
            if S[i-1] == S[i]:
                if flag:
                    ans.append(string.popleft())
                else:
                    ans.append(string.pop())
            else:
                if flag:
                    ans.append(string.pop())
                else:
                    ans.append(string.popleft())
                flag = not flag   
        ans.append(string.pop())
        return ans
        """
        It can be simplified as using low and high index, but I want to practice and use deque here
        :type S: str
        :rtype: List[int]
        """