423 · Valid Parentheses - LintCode

# Description

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.

# Example

Example 1:

Input: "([)]"
Output: False

Example 2:

Input: "()[]{}"
Output: True

Challenge

Use O(n) time, n is the number of parentheses.

	public class Solution {
	/**
	* @param s: A string
	* @return: whether the string is a valid parentheses
	*/
	public boolean isValidParentheses(String s) {
	if(s.length() <= 1 \|\| s == null){
	return false;
	}
	Stack<Character> stack = new Stack<>();

	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(!stack.empty() && stack.peek() == leftOf(s.charAt(i))){
	stack.pop();
	} else {
	return false;
	}
	}
	}
	System.out.println(stack.size());
	return stack.empty();

	}
	private char leftOf(char c){
	if(c == '}') return '{';
	if(c == ')') return '(';
	return '[';

	}
	}