class Solution {
public:
int minLength(string s) {
string stk = " ";//放一个空字符,不需要特判栈是否为空,答案减一即可
for (auto& c: s) {
if (c == 'B' && stk.back() == 'A' || c == 'D' && stk.back() == 'C')
stk.pop_back();
else
stk.push_back(c);
}
return stk.size() - 1;
}
};