Valid Parentheses

题目：

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

分析：

看到题目想到用stack，但是别忘了结尾要判断myStack.isEmpty()

解法：

public class Solution {
    /**
     * @param s A string
     * @return whether the string is a valid parentheses
     */
    public boolean parenMatched(char lhs, char rhs) {
        if (rhs == ')') {
            return lhs == '(';
        } else if (rhs == ']') {
            return lhs == '[';
        } else {
            return lhs == '{';
        }
    } 

    public boolean isValidParentheses(String s) {
        // Write your code here
        Stack<Character> myStack = new Stack<Character>();
        for (int i = 0; i < s.length(); i++) {
            char curr = s.charAt(i);
            if (curr == '(' || curr == '[' || curr == '{') {
                myStack.push(curr);
            } else {
                if (myStack.empty() ) {
                    return false;
                } else {
                    if (!parenMatched(myStack.pop(),curr ) ) {
                        return false;
                    }
                }
            }
        }
        return myStack.empty();
    }
}