Generate Parentheses

public class Solution {
    public ArrayList<String> generateParenthesis(int n) {
        // IMPORTANT: Please reset any member data you declared, as
        // the same Solution instance will be reused for each test case.
        ArrayList<String> result = new ArrayList<String>();
        StringBuilder builder = new StringBuilder();
        generate(result, builder, n, n);
        return result;
    }
    private void generate(ArrayList<String> result, StringBuilder builder, int start, int end){
        if(start == 0 && end == 0){
            result.add(builder.toString());
            return;
        }
        if(start > 0){
            builder.append('(');
            generate(result, builder, start-1, end);
            builder.deleteCharAt(builder.length()-1);
        }
        if(end > start){
            builder.append(')');
            generate(result, builder, start, end-1);
            builder.deleteCharAt(builder.length()-1);
        }
    }
}