1622. Fancy Sequence

# Time:  O(1)
# Space: O(n)

MOD = 10**9+7

class Fancy(object):

    def __init__(self):
        self.__arr = []
        self.__ops = [[1, 0]]

    def append(self, val):
        """
        :type val: int
        :rtype: None
        """
        self.__arr.append(val)
        self.__ops.append(self.__ops[-1][:])

    def addAll(self, inc):
        """
        :type inc: int
        :rtype: None
        """
        self.__ops[-1][1] = (self.__ops[-1][1]+inc) % MOD

    def multAll(self, m):
        """
        :type m: int
        :rtype: None
        """
        self.__ops[-1] = [(self.__ops[-1][0]*m) % MOD, (self.__ops[-1][1]*m) % MOD]

    def getIndex(self, idx):
        """
        :type idx: int
        :rtype: int
        """
        if idx >= len(self.__arr):
            return -1
        a1, b1 = self.__ops[idx]
        a2, b2 = self.__ops[-1]
        a = a2*pow(a1, MOD-2, MOD)%MOD  # O(logMOD), we treat it as O(1) here
        b = (b2 - b1*a) % MOD
        return (self.__arr[idx]*a + b) % MOD


# Time:  O(1)
# Space: O(n)
class Fancy2(object):

    def __init__(self):
        self.__arr = []
        self.__op = [1, 0]

    def append(self, val):
        """
        :type val: int
        :rtype: None
        """
        self.__arr.append((val-self.__op[1])*pow(self.__op[0], MOD-2, MOD)%MOD)  # O(logMOD), we treat it as O(1) here

    def addAll(self, inc):
        """
        :type inc: int
        :rtype: None
        """
        self.__op[1] = (self.__op[1]+inc) % MOD

    def multAll(self, m):
        """
        :type m: int
        :rtype: None
        """
        self.__op = [(self.__op[0]*m) % MOD, (self.__op[1]*m) % MOD]

    def getIndex(self, idx):
        """
        :type idx: int
        :rtype: int
        """
        if idx >= len(self.__arr):
            return -1
        a, b = self.__op
        return (self.__arr[idx]*a + b) % MOD

Solution from kamyu104/LeetCode-Solutions · MIT