def flatten(arr) -> list:
    ''' Flattens array'''
    return flatten(arr[0]) + (flatten(arr[1:]) if len(arr) > 1 else []) if type(arr) is list else [arr]

def sum_dict(arr) -> dict:
    ''' Sums array of dicts: [{a:3,b:3},{b:1}] -> {a:3,b:4} '''
    result = arr[0]
    for hash in arr[1:]:
         for key in hash.keys():
            if key in result:
                result[key] = result[key] + hash[key]
            else:
                result[key] = hash[key]
    return result