CTCI 9.6

Implement an algorithm to print all valid (i.e., properly opened and closed) combinations of n-pairs of parentheses.

CTCI 9.6.java

public static ArrayList<String> nPairsParentheses(int n){
    ArrayList<String> output = new ArrayList<>();
    nPairsParentheses(n, 0, new StringBuffer(), output);
    return output;
}

public static void nPairsParentheses(int remindLeft, int remindRight, StringBuffer byfar, ArrayList<String> output){
    if(remindLeft == 0 && remindRight == 0) output.add(byfar.toString());
    if(remindLeft > 0){
        byfar.append("(");
        nPairsParentheses(remindLeft - 1, remindRight + 1, byfar, output);
        byfar.deleteCharAt(byfar.length() - 1);
    }
    if(remindRight > 0){
        byfar.append(")");
        nPairsParentheses(remindLeft, remindRight - 1, byfar, output);
        byfar.deleteCharAt(byfar.length() - 1);
    }
}