Minimum String Length After Removing Substrings

class Solution {
public:
    int minLength(string s) {
        string st;
        st.reserve(s.size());
        for (char c : s) {
            if (!st.empty() && ((st.back() == 'A' && c == 'B') || (st.back() == 'C' && c == 'D'))) {
                st.pop_back();
            } else {
                st.push_back(c);
            }
        }
        return st.size();
    }
};

func minLength(s string) int {
    st := make([]byte, 0, len(s))
    for i := 0; i < len(s); i++ {
        c := s[i]
        if len(st) > 0 {
            top := st[len(st)-1]
            if (top == 'A' && c == 'B') || (top == 'C' && c == 'D') {
                st = st[:len(st)-1]
                continue
            }
        }
        st = append(st, c)
    }
    return len(st)
}

class Solution:
    def minLength(self, s: str) -> int:
        st: list[str] = []
        for c in s:
            if st and ((st[-1] == 'A' and c == 'B') or (st[-1] == 'C' and c == 'D')):
                st.pop()
            else:
                st.append(c)
        return len(st)

function minLength(s) {
    const st = [];
    for (const c of s) {
        const top = st[st.length - 1];
        if (st.length && ((top === 'A' && c === 'B') || (top === 'C' && c === 'D'))) {
            st.pop();
        } else {
            st.push(c);
        }
    }
    return st.length;
}

class Solution {
    public int minLength(String s) {
        StringBuilder st = new StringBuilder();
        for (int i = 0; i < s.length(); i++) {
            char c = s.charAt(i);
            int len = st.length();
            if (len > 0) {
                char top = st.charAt(len - 1);
                if ((top == 'A' && c == 'B') || (top == 'C' && c == 'D')) {
                    st.deleteCharAt(len - 1);
                    continue;
                }
            }
            st.append(c);
        }
        return st.length();
    }
}

function minLength(s: string): number {
    const st: string[] = [];
    for (const c of s) {
        const top = st[st.length - 1];
        if (st.length && ((top === 'A' && c === 'B') || (top === 'C' && c === 'D'))) {
            st.pop();
        } else {
            st.push(c);
        }
    }
    return st.length;
}