public IList <string> LetterCasePermutation(string S)
{
//先构造一棵树
BinaryStringTreeNode root = new BinaryStringTreeNode("");
Queue <BinaryStringTreeNode> queue = new Queue <BinaryStringTreeNode>();
queue.Enqueue(root);
foreach (char c in S)
{
char lower, upper;
if ((c >= 'a' && c <= 'z') || (c >= 'A' && c <= 'Z'))
{
if (c >= 'a' && c <= 'z')
{
lower = c;
upper = (char)(c - 32);
}
else
{
lower = (char)(c + 32);
upper = c;
}
}
else
{
lower = c;
upper = c;
}
List <BinaryStringTreeNode> lst = new List <BinaryStringTreeNode>();
while (queue.Count > 0)
{
BinaryStringTreeNode node = queue.Dequeue();
node.left = new BinaryStringTreeNode(node.val + lower.ToString());
lst.Add(node.left);
if (lower != upper)
{
node.right = new BinaryStringTreeNode(node.val + upper.ToString());
lst.Add(node.right);
}
}
foreach (var node in lst)
{
queue.Enqueue(node);
}
lst.Clear();
}
List <string> res = new List <string>();
while (queue.Count > 0)
{
res.Add(queue.Dequeue().val);
}
res.Sort();
return(res);
}
public BinaryStringTreeNode(string val)
{
this.val = val;
left = null;
right = null;
}