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.
括号匹配，遍历ｓｔｒｉｎｇ，碰到左括号把左括号入栈，碰到右括号出栈，判断出栈的字符和右括号是否匹配。
public class Solution {
public boolean isValid(String s) {
Stack<Character> stack = new Stack<Character>();
for (int i = 0; i < s.length(); i++) {
switch (s.charAt(i)) {
case ‘(‘:
case ‘{‘:
case ‘[‘:
stack.push(s.charAt(i));
break;
case ‘)‘:
if (stack.empty() || stack.pop() != ‘(‘) {
return false;
}
break;
case ‘}‘:
if (stack.empty() || stack.pop() != ‘{‘) {
return false;
}
break;
case ‘]‘:
if (stack.empty() || stack.pop() != ‘[‘) {
return false;
}
break;
}
}
if (stack.empty()) {
return true;
} else {
return false;
}
}
}
原文：http://www.cnblogs.com/yuchenkit/p/7169505.html