52. Bracket sequence

 

Title description

Given a string containing only the characters'(',')','{','}','[' and']', determine whether the given string is a legal bracket sequence. The
brackets must be correct The order is closed, "()" and "()[]{}" are both legal bracket sequences, but "(]" and "([)]" are illegal.

Example 1

enter

"["

return value

false

Example 2

enter

"[]"

return value

true

Code implementation :

import java.util.*;


public class Solution {
    /**
     * 
     * @param s string字符串 
     * @return bool布尔型
     */
    public boolean isValid (String s) {
        char[] arr = s.toCharArray();
        Stack<Character> stack = new Stack<>();
        for (char a : arr) {
            if (a == '(' || a == '{' || a == '[') {
                stack.push(a);
            } else {
                if (stack.empty()) {
                    return false;
                }
                if ((stack.peek() == '(' && a == ')') ||
                    (stack.peek() == '{' && a == '}') ||
                    (stack.peek() == '[' && a == ']')) {
                    stack.pop();
                }
            }
        }
        if (stack.empty()) {
            return true;
        } else {
            return false;
        }
    }
}