3223. Minimum Length of String After Operations

You are given a string s.

You can perform the following process on s any number of times:

• Choose an index i in the string such that there is at least one character to the left of index i that is equal to s[i], and at least one character to the right that is also equal to s[i].
• Delete the closest character to the left of index i that is equal to s[i].
• Delete the closest character to the right of index i that is equal to s[i].

Return the minimum length of the final string s that you can achieve.

class Solution {
public:
    int minimumLength(string s) {
        unordered_map<char,int> freq;
        for(auto& ch : s) freq[ch]++;
        int res = 0;
        for(auto& [_,cnt] : freq) {
            res += (cnt % 2 ? 1 : 2);
        }
        return res;
    }
};