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<>();
        for (int i = 0; i < s.length(); i++) {
            char cha = s.charAt(i);
            char pre ;
            switch (cha) {
                case '(':
                case '[':
                case '{':
                    stack.push(cha);
                    break;
                case ')':
                    if (stack.isEmpty()) {
                        return false;
                    }
                    pre = stack.pop();
                    if (pre != '(') {
                        return false;
                    }
                    break;
                case ']':
                    if (stack.isEmpty()) {
                        return false;
                    }
                    pre = stack.pop();
                    if (pre != '[') {
                        return false;
                    }
                    break;
                case '}':
                    if (stack.isEmpty()) {
                        return false;
                    }
                    pre = stack.pop();
                    if (pre != '{') {
                        return false;
                    }
                    break;
                default:
                    return false;
            }
        }
        if (stack.isEmpty()) {
            return true;
        } else {
            return false;
        }
    }
}