题解 | #有效括号序列#

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 isValid (String s) {
        // write code here
        int len = s.length();
        if (len == 0) return true;
        if (len == 1) return false;
        if (len % 2 != 0) return false;
        Stack<Character> stack = new Stack<Character>();
        for (int i = 0; i < len; i++) {
            Character c = s.charAt(i);
            if (!isValid(c)) return false;
            if (isLeft(c)) {
                stack.push(c);
            } else {
                if(stack.isEmpty()) return false;
                //看最近的一个是否与它相配
                if(!isPair(c, stack.pop())){
                    return false;
                }
            }
        }
        return stack.isEmpty();
    }

    private boolean isValid(Character c) {
        return c == '(' || c == ')' || c == '{' || c == '}' || c == '[' || c == ']';
    }

    private boolean isLeft(Character c) {
        return c == '('  || c == '{'  || c == '[' ;
    }

    private boolean isPair(Character c, Character d) {
        if (c == ')'  ) {
            return d == '(';
        } else if (c == '}'  ) {
            return d == '{';
        } else {
            return d == '[';
        }
    }

}