Jump Game IV

class Solution(object):
    def minJumps(self, arr):
        """
        :type arr: List[int]
        :rtype: int
        """
        n = len(arr)
        hm = {}
        for i, e in enumerate(arr):
            hm.setdefault(e, []).append(i)

        #bfs
        vis = set([-1,0])
        dq = deque([(0, 0)])
        while dq:
            cn, cd = dq.pop()

            if cn == n-1:
                return cd

            if cn-1 not in vis:
                vis.add(cn-1)
                dq.appendleft((cn-1, cd+1))

            if cn+1 not in vis:
                vis.add(cn+1)
                dq.appendleft((cn+1, cd+1))

            for i in hm[arr[cn]]:
                if i not in vis:
                    vis.add(i)
                    dq.appendleft((i, cd+1))
'''since all indices with value arr[cn] has been added to the que, we erase the hash value for arr[cn] so for all these indices added to the queue the for loop is not executed(as it will never satisfy unvisited condition anyways, if not erased)'''
            hm[arr[cn]] = [] #imp to avoid tle... equivalent classes

        return -1