https://oj.leetcode.com/problems/valid-parentheses/
http://fisherlei.blogspot.com/2013/01/leetcode-valid-parentheses.html
public class Solution {
public boolean isValid(String s)
{
if (s == null)
return true;
Stack<Character> stack = new Stack<>();
for (char c : s.toCharArray())
{
if (c == ‘(‘ || c == ‘[‘ || c == ‘{‘)
{
stack.push(c);
}
else if (c == ‘)‘)
{
if (stack.isEmpty() || stack.pop() != ‘(‘)
return false;
}
else if (c == ‘]‘)
{
if (stack.isEmpty() || stack.pop() != ‘[‘)
return false;
}
else if (c == ‘}‘)
{
if (stack.isEmpty() || stack.pop() != ‘{‘)
return false;
}
}
return stack.empty();
}
}[LeetCode]20 Valid Parentheses
原文：http://7371901.blog.51cto.com/7361901/1598419