[leetcode]20. Valid Parentheses

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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.

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主要就是对栈的理解。java有原生的栈的支持，golang没有，这里就不写go的版本了。

public class Solution {    public boolean isValid(String s) {        if(s==null||"".equals(s)||s.length()==1){            return false;        }        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 if(s.charAt(i)=='}'){                if(!stack.empty()&&stack.peek()=='{'){                    stack.pop();                }else{                    return false;                }            }else if(s.charAt(i)==']'){                if(!stack.empty()&&stack.peek()=='['){                    stack.pop();                }else{                    return false;                }            }else if(s.charAt(i)==')'){                if(!stack.empty()&&stack.peek()=='('){                    stack.pop();                }else{                    return false;                }            }        }        if(!stack.empty()){            return false;        }else{            return true;        }    }}

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