题解 | #牛群的配对#

import java.util.*;


public class Solution {
    /**
     * 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
     *
     *
     * @param s string字符串
     * @return bool布尔型
     */
    public boolean isValidPairing (String s) {
        Deque<Character> stack = new LinkedList<>();
        for (char c : s.toCharArray()) {
            if (stack.isEmpty()) {
                stack.push(c);
            } else if ((c == 'B' && stack.peek() == 'A') || (c == 'D' &&
                       stack.peek() == 'C')) {
                stack.pop();
            } else {
                stack.push(c);
            }
        }
        return stack.isEmpty();
    }
}