def backtracking(data, candidates, result, index = 0):
    if index == len(data):
        result.append(tuple(data))
    else:
        next_index = index + 1
        for iter in range(len(candidates)):
            candidate = candidates[iter]
            if candidate:
                data[index] = candidate
                candidates[iter] = None
                backtracking(data, candidates, result, next_index)
                candidates[iter] = candidate
def permutations(s):
    result = []
    candidates = [i for i in s]
    backtracking([None for i in s], candidates, result)

    return result