public static ParensResult GenerateParens(int count)
{
if (count < 0)
{
return(null);
}
RecursionCount rc = new RecursionCount();
char[] str = new char[count * 2];
List <string> list = new List <string>();
AddParen(list, count, count, str, 0, rc);
return(new ParensResult()
{
list = list,
recursionCount = rc.count
});
}
private static void AddParen(List <string> list,
int leftRem, int rightRem, char[] str, int index, RecursionCount rc)
{
rc.count++;
if (leftRem < 0 || rightRem < leftRem)
{
// invalid state
return;
}
if (leftRem == 0 && rightRem == 0)
{
list.Add(new string(str));
return;
}
str[index] = '(';
AddParen(list, leftRem - 1, rightRem, str, index + 1, rc);
str[index] = ')';
AddParen(list, leftRem, rightRem - 1, str, index + 1, rc);
}
private static void AddParen2Count(List <string> list,
int leftRemaining, int rightAvailable, char[] str, int index, RecursionCount rc)
{
rc.count++;
if (leftRemaining == 0 && rightAvailable == 0)
{
list.Add(new string(str));
return;
}
if (leftRemaining > 0)
{
str[index] = '(';
AddParen2Count(list, leftRemaining - 1, rightAvailable + 1, str, index + 1, rc);
}
if (rightAvailable > 0)
{
str[index] = ')';
AddParen2Count(list, leftRemaining, rightAvailable - 1, str, index + 1, rc);
}
}
