LeetCode - Valid Parentheses

题目：

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.

思路：

用栈来解决。

package ds;

import java.util.Stack;

public class ValidParentheses {

public boolean isValid(String s) {
Stack<Character> stack = new Stack<Character>();
int len = s.length();
for (int i = 0; i < len; ++i) {
char c = s.charAt(i);
switch (c) {
case '(':

case '[':

case '{':
stack.push(c);
break;
case ')':
if (stack.isEmpty() || stack.pop() != '(')
return false;
break;
case ']':
if (stack.isEmpty() || stack.pop() != '[')
return false;
break;
case '}':
if (stack.isEmpty() || stack.pop() != '{')
return false;
break;
}
}

return stack.isEmpty();
}

public static void main(String[] args) {
// TODO Auto-generated method stub
ValidParentheses v = new ValidParentheses();
// Test case 1
System.out.println(v.isValid("()[]}"));
// Test case 2
System.out.println(v.isValid("("));
}

}