题解 | #有效括号序列#

import java.util.*;


public class Solution {
    /**
     *
     * @param s string字符串
     * @return bool布尔型
     */
    public boolean isValid (String s) {
        // write code here
        Stack<Character> stack = new Stack<Character>();
        for (int i = 0; i < s.length(); i++) {
            if (s.charAt(i) == '{' || s.charAt(i) == '(' || s.charAt(i) == '[') {
                stack.push(s.charAt(i));
            } else {
                if (s.charAt(i) == ')') {
                    if (stack.isEmpty() || stack.peek() != '(') {
                        return false;
                    } else {
                        stack.pop();
                    }
                }
                if (s.charAt(i) == '}') {
                    if (stack.isEmpty() || stack.peek() != '{') {
                        return false;
                    } else {
                        stack.pop();
                    }
                }
                if (s.charAt(i) == ']') {
                    if (stack.isEmpty() || stack.peek() != '[') {
                        return false;
                    } else {
                        stack.pop();
                    }
                }
            }
        }
        return stack.isEmpty();
    }
}