def count_subsequences(s):
"""
Counts the number of subsequences of a given string containing all unique characters.
Args:
s (str): The given string.
Returns:
int: The number of subsequences of s containing all unique characters.
"""
# Check if the given string is empty.
if not s:
return 0
# Create a dictionary to store the index of the last occurrence of each character in s.
last_occurrence =
for i in range(len(s)):
last_occurrence[s[i]] = i
# Create a variable to store the number of subsequences of s containing all unique characters.
num_subsequences = 0
# Create a variable to store the index of the last character added to a subsequence.
last_added = -1
# Iterate over the characters in s.
for i in range(len(s)):
# If the current character is the last occurrence of itself in s,
# then it can be added to a subsequence.
if i == last_occurrence[s[i]]:
# Add the current character to the subsequence.
num_subsequences += 1
last_added = i
# Otherwise, the current character cannot be added to a subsequence.
else:
# Update the index of the last occurrence of the current character in s.
last_occurrence[s[i]] = i
# If the current character is not the last character added to a subsequence,
# then reset the count of subsequences.
if i != last_added + 1:
num_subsequences = 0
# Return the number of subsequences of s containing all unique characters.
return num_subsequences
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