【栈】20.有效的括号

题目

法1：栈

栈的基础知识介绍：http://www.nhooo.com/java/java-stack.html
必须掌握之算法

Python

class Solution:
    def isValid(self, s: str) -> bool:
        stack = collections.deque()
        for i in range(len(s)):
            if len(stack) == 0:
                stack.append(s[i])
            elif s[i] == ')' and stack[-1] == '(':
                stack.pop()
            elif s[i] == '}' and stack[-1] == '{':
                stack.pop()  
            elif s[i] == ']' and stack[-1] == '[':
                stack.pop()  
            else:
                stack.append(s[i])               

        return True if len(stack) == 0 else False

Java

class Solution {
    public boolean isValid(String s) {
        char[] array = s.toCharArray();
        Stack<Character> stack = new Stack<>();
        for (int i = 0; i < array.length; ++i) {
            if (array[i] == '(' || array[i] == '[' || array[i] == '{') {
                stack.push(array[i]);
            } else if (!stack.isEmpty() 
                        && (array[i] == ')' && stack.peek() == '(' 
                            || array[i] == ']' && stack.peek() == '[' 
                            || array[i] == '}' && stack.peek() == '{')) {
                stack.pop();
            } else {
                return false;
            }
        }

        return stack.isEmpty();
    }
}