C# 代码
public class Solution {
public int MinLength(string s) {
int n = s.Length;
Stack<char> stack = new Stack<char>();
stack.Push('#');
foreach (char ch in s){
if ((ch == 'B' && stack.Peek() == 'A') || (ch == 'D' && stack.Peek() == 'C')){
stack.Pop();
}
else{
stack.Push(ch);
}
}
return stack.Count - 1;
}
}