20 Valid Parentheses

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.

判断一个括号字符串是否是有效

public class Solution {

public boolean isValid(String s) {
Stack<Integer> stk = new Stack<Integer>();
for (int i = 0; i < s.length(); ++i) {
int pos = "(){}[]".indexOf(s.substring(i, i + 1));
if (pos % 2 == 1) {
if (stk.isEmpty() || stk.pop() != pos - 1)
return false;
} else {
stk.push(pos);
}
}
return stk.isEmpty();
}
}