423. Valid Parentheses【LintCode java】

標籤：size   wrap   write   als   class   char   idp   bsp   app   

Description

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

Example

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

Challenge

O(n)的時間，n為括弧的個數

解題：括弧匹配問題，用棧來做較為簡單，代碼如下：

public class Solution {    /**     * @param s: A string     * @return: whether the string is a valid parentheses     */    public boolean isValidParentheses(String s) {        // write your code here        Stack<Character>stack = new Stack<Character>();        for(int i = 0; i < s.length(); i++){            if(s.charAt(i) == ‘(‘ || s.charAt(i) == ‘{‘ || s.charAt(i) == ‘[‘){                stack.push(s.charAt(i));            }else{ //pop前要先檢查棧是不是空的                if(!stack.isEmpty()){                    switch(s.charAt(i)){                    case ‘)‘:                        if(!stack.pop().equals(‘(‘)){                            return false;                        }                        break;                    case ‘]‘:                        if(!stack.pop().equals(‘[‘)){                            return false;                        }                        break;                    case ‘}‘:                        if(!stack.pop().equals(‘{‘)){                            return false;                        }                        break;                    }                }else{                    return false;                }            }        }        if(stack.isEmpty()){            return true;        }else{            return false;        }    }}

 

423. Valid Parentheses【LintCode java】