Jump Game III

#iterative version
class Solution(object):
    def canReach(self, arr, start):
        """
        :type arr: List[int]
        :type start: int
        :rtype: bool
        """
        dq = deque([start])

        while dq:
            #for dfs
            curr = dq.pop()

            #for bfs
            #curr = dq.popleft()

            #1&2 conditions can be checked either when the position is seen (i.e added to dq) or when its processed (i.e removed from dq)
            if not 0 <= curr < len(arr) or arr[curr] < 0:#1
                continue

            if arr[curr] == 0:#2, no further jumps, as 0 is additive n subtractive identity
                return True

            # -ve sign used as insitu visited marker; also, a+b = a-(-b) and a-b = a+(-b)
            arr[curr] *= -1

            dq.append(curr + arr[curr])
            dq.append(curr - arr[curr])

        return False

#recursive version
'''
class Solution(object):
    def canReach(self, arr, start):
        """
        :type arr: List[int]
        :type start: int
        :rtype: bool
        """
        if not 0<=start<len(arr) or arr[start] < 0:
            return False

        arr[start] *= -1

        # due to SHORT CIRCUIT(LAZY) EVALUATION sub expressions following true subexp. are not evaluated.
        return arr[start] == 0 or self.canReach(arr, start-arr[start]) or self.canReach(arr, start+arr[start])
'''