flip-game.py

# Time:  O(c * n + n) = O(n * (c+1))
# Space: O(n)

class Solution(object):
    def generatePossibleNextMoves(self, s):
        """
        :type s: str
        :rtype: List[str]
        """
        res = []
        i, n = 0, len(s) - 1
        while i < n:                                    # O(n) time
            if s[i] == '+':
                while i < n and s[i+1] == '+':          # O(c) time
                    res.append(s[:i] + '--' + s[i+2:])  # O(n) time and space
                    i += 1
            i += 1
        return res


# Time:  O(c * m * n + n) = O(c * n + n), where m = 2 in this question
# Space: O(n)
# This solution compares O(m) = O(2) times for two consecutive "+", where m is length of the pattern
class Solution2(object):
  def generatePossibleNextMoves(self, s):
      """
      :type s: str
      :rtype: List[str]
      """
      return [s[:i] + "--" + s[i+2:] for i in xrange(len(s) - 1) if s[i:i+2] == "++"]