1079 Letter Tile Possibilities

Code

Python3

def numTilePossibilities(self, T: str) -> int:
  count = Counter(T)
 
  def bt():
    total = 0
 
    for c in count:
      if count[c] > 0:
        count[c] -= 1
        total += 1 + bt()
        count[c] += 1
 
    return total

Big O Analysis

• Runtime

  The runtime complexity here is $O(2^N)$ since we are checking all permutations of the string.

• Memory

  The memory usage is $O(N)$ since we use the collections.Counter object to store character frequencies.

— A

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