题解 | #有效括号序列# #Java# 简单，直觉

import java.util.*;


public class Solution {
    /**
     * 
     * @param s string字符串 
     * @return bool布尔型
     */
    public boolean isValid (String s) {
        Stack<Character> stack = new Stack<>();
        for(char c: s.toCharArray()) {
            if(stack.isEmpty()) { //放入第一个字符并直接跳入下一轮
                stack.push(c);
                continue;
            }
            char top = stack.peek(); //查看堆顶是否能与当前符号匹配。若匹配，则去除堆顶
            if(c == ')' && top == '(') stack.pop();
            else if(c == ']' && top == '[') stack.pop();
            else if(c == '}' && top == '{') stack.pop();
            else stack.push(c); //不匹配，则压入
        }

        return stack.isEmpty(); //全部匹配时，堆被清空
    }
}