def gen_candidates(part_sol, data):
    result = []
    for i in data:
        if i not in part_sol:
            result.append(i)
    return result

def backtracking(part_sol, part_sol_len, data, data_len, result):
    if part_sol_len == data_len:
        result.append(part_sol)
    else:
        new_part_sol = [i for i in part_sol]
        candidates = gen_candidates(part_sol, data)
        for candidate in candidates:
            new_part_sol.append(candidate)
            backtracking(new_part_sol, part_sol_len + 1, data, data_len, result)
def permutations(s):