括号匹配

class Solution {
    public boolean isValid(String s) {
        if(s==null||s.length()==0){
            return true;
        }
        //将字符串转换为char[]
        char[] c=s.toCharArray();
        Stack<Character> stack=new Stack<Character>();
        for(int i=0;i<c.length;i++){
            if(c[i]=='('||c[i]=='{'||c[i]=='['){
                stack.push(c[i]);
            }
            if(c[i]==')'){
            //这个地方判断条件一定要注意顺序
                if(stack.isEmpty()||stack.pop()!='('){
                    return false;
                }
            }
           if(c[i]=='}'){
                if(stack.isEmpty()||stack.pop()!='{'){
                     return false;
                }
            }
            if(c[i]==']'){
                if(stack.isEmpty()||stack.pop()!='['){
                        return false;
                }
            }
        }
        return stack.isEmpty();
    }
}