Remove Outermost Parentheses

用一个count来计算”(“和”)”的差，0就是最外边的。

class Solution {
    public String removeOuterParentheses(String S) {
        int count = 0; // count the diff between "(" and ")"
        StringBuffer res = new StringBuffer();
        StringBuffer tmp = new StringBuffer();
        for(int i = 0 ; i < S.length(); i++) {
            if(S.charAt(i) == '(') 
                count++;
            else if(S.charAt(i) == ')')
                count--;
            tmp.append(S.charAt(i)); 
            if(count == 0){ // if it is outter
                tmp.deleteCharAt(0); // remove first 
                tmp.deleteCharAt(tmp.length()-1);//remove last
                res.append(tmp);
                tmp.setLength(0); //reset tmp
            }
        }
        return res.toString();
    }
}