Is Unique

Implement an algorithm that determines if all characters in a String are unique.

Once you solve it, how would you implement it if you can't use other additional data structures like Arrays, etc?

👉 Link here to the repo where you can solve the problem

👌 Tips

Try a HashTable

Could you try it with a BitVector?

Could you solve it in a time 0(N log N)?

👊 Solution 1

A very simple solution would be to create an array of booleans, where we would get the character's position in the alphabet, and in that position in the booleans array we would convert it to true. If true already exists in that array position, it means that we have repeated character.

boolean isUnique(String s) {
    if (s.length() > 128) return false;

    boolean[] set = new boolean[128];
    for (int i = 0; i < s.length(); i++) {
        int v = s.charAt(i);
        if (set[v]) {
            return false;
        }
        set[v] = true;
    }
    return true;
}

The complexity of this solution is 0(N), where N is string.length().

👊 Solution 2

We could reduce the use of space using a BitVector in the form of an Int.

If we assume that we will only use the letters "a" to "z" in lowercase letters, we will not need more than 28 flags, which are in an Int (28 bits).

This solution is very similar to the previous one, but instead of an Array with 128 spaces, we use a BitWise Operator to light the flags from 0s to 1s.

boolean isUniqueBitVector(String s) {
    int checker = 0;
    for (int i = 0; i < s.length(); i++) {
        int v = s.charAt(i);
        if ((checker & (1 << v)) > 0) {
            return false;
        }
        checker |= (1 << v);
    }
    return true;
}

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Borrowed question from the book "Cracking the coding interview"