# tip selection pseudocode
def pick_tip(tangle, tips):
    tovisit = queue(tips.copy())

    while !tovisit.empty():
        tx = tovisit.poll()
        tx.weight = sum(tx.approvees.weights) + 1
        if tx.depth < maxdepth:
            tovisit.push(tx.branch, tx.trunk)

    walktx = random tx in tangle where depth == maxdepth
    while walktx not in tips:
        walktx = weighted_random(walktx.approvees)

    return walktx