frontier = []

frontier.append([tup_node,""])

allNodes = set()

while len(frontier) != 0:

node = frontier.pop()

tnode = node[0]

res = isGoal(tnode,False)

if res == 1:

return "".join(node[1])

elif res == -1:

return None

allNodes.add(tnode)

if len(node[1]) < dep_limit:

for idx, child in enumerate(reversed(getAllChildren(tnode,allNodes))):

if child != None:

frontier.append([child, node[1] + seq_one[-(idx+1)]])