Leetcode每日一题_20
public static boolean isValid(String s) {//o(n) o(n)
    if(s==null||s.length()==0)return true;
&nbsp;&nbsp;&nbsp;&nbsp;Stack<Character>&nbsp;stack=new&nbsp;Stack<>();
&nbsp;&nbsp;&nbsp;&nbsp;for(Character&nbsp;c:s.toCharArray())&nbsp;{
&nbsp;&nbsp;&nbsp;&nbsp;if&nbsp;(c=='(')&nbsp;{
stack.push(')');
&nbsp;&nbsp;&nbsp;&nbsp;}
else&nbsp;if&nbsp;(c=='[')&nbsp;{
stack.push(']');
}
else&nbsp;if&nbsp;(c=='{')&nbsp;{
stack.push('}');
}else&nbsp;{
if&nbsp;(stack.isEmpty()||stack.pop()!=c)&nbsp;{
return&nbsp;false;
}
}
&nbsp;&nbsp;&nbsp;&nbsp;}
&nbsp;&nbsp;&nbsp;&nbsp;return&nbsp;stack.isEmpty();
}