2716. Minimize String Length

Given a 0-indexed string s, repeatedly perform the following operation any number of times:

• Choose an index i in the string, and let c be the character in position i. Delete the closest occurrence of c to the left of i (if any) and the closest occurrence of c to the right of i (if any).

Your task is to minimize the length of s by performing the above operation any number of times.

Return an integer denoting the length of the minimized string.

class Solution {
public:
    int minimizedStringLength(string s) {
        unordered_set<char> us;
        for(auto& ch : s) us.insert(ch);
        return us.size();
    }
};