20. Valid Parentheses

来源：互联网发布：apache 2.0 开源协议编辑：程序博客网时间：2024/05/22 17:24

Given a string containing just the characters '(', ')', '{', '}', '[' and ']', determine if the input string is valid.

The brackets must close in the correct order, "()" and "()[]{}" are all valid but "(]" and "([)]" are not.

判断括号的合法性。用栈就可以搞定。

一开始用了一个HashMap用来做右括号对左括号的映射，后来看到网友有更好的表达方式，就采用了。程序如下所示：

class Solution {    public boolean isValid(String s) {          ArrayDeque<Character> stack = new ArrayDeque<>();        int len = s.length();        // Map<Character, Character> map = new HashMap<>();        // map.put(')', '(');        // map.put(']', '[');        // map.put('}', '{');        char ch;        for (int i = 0; i < len; ++ i){            ch = s.charAt(i);            if (ch == '('){                stack.push(')');            }            else if (ch == '['){                stack.push(']');            }            else if (ch == '{'){                stack.push('}');            }            else {                if (stack.isEmpty()||stack.pop() != ch){                    return false;                }            }        }        return stack.isEmpty();    }}

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