Implementing an algorithm to determine if a string has all unique characters [closed]

Answer 1

Your solution is not incorrect but your variable dict is not actually a dictionary which means it has to do a linear search to check for the character. The solution from the book does the check in constant time. I will say that the other solution is obnoxiously unreadable because it uses setting the bits in a number to check if the char is unique or not

Answer 2

your implementation takes O(n2), author takes O(n). In your implementation, " if c in uchars:" , when it check if c in this array, it will have to go through the whole array, it takes time. So yours is not better than author's...

Answer 3

The original question is along the lines of: Implement an algorithm to determine if a string has all unique characters. What if you cannot use additional data structures?

Focus on the second sentence, It says we cannot use additional data structures, i.e you need to consider the space complexity of your solution. Your solution uses an array and therefore is not meeting the questions criteria.

Answer 4

Here is how I would write this:

def unique(s):
    return len(set(s)) == len(s)

Strings are iterable so you can pass your argument directly to set() to get a set of the characters from the string (which by definition will not contain any duplicates). If the length of that set is the same as the length of the original string then you have entirely unique characters.

Your current approach is fine and in my opinion it is much more Pythonic and readable than the version proposed by the author, but you should change uchars to be a set instead of a list. Sets have O(1) membership test so c in uchars will be considerably faster on average if uchars is a set rather than a list. So your code could be written as follows:

def unique(s):
    uchars = set()
    for c in s:
        if c in uchars:
            return False
        uchars.add(c)
    return True

This will actually be more efficient than my version if the string is large and there are duplicates early, because it will short-circuit (exit as soon as the first duplicate is found).

Answer 5

Beautiful is better than ugly.

Your approach is perfectly fine. This is python, when there are a bajillion ways to do something. (Yours is more beautiful too :)). But if you really want it to be more pythonic and/or make it go faster, you could use a set, as F.J's answer has described.

The second solution just looks really hard to follow and understand.

(PS, dict is a built-in type. Don't override it :p. And string is a module from the standard library.)

Answer 6

str = raw_input("Enter string: ")


def isUnique():
    test_dict = dict()
    is_unique = True
    for c in str:
        if(not test_dict.get(c, False)):
            test_dict[c] = c
        else:
            is_unique = False
            break
    if is_unique:
        return "String is unique"
    else:
        return "String is not unique"

print(isUnique())