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Check if All Characters Have Equal Number of Occurrences

Number: 2053

Difficulty: Easy

Paid? No

Companies: Bloomberg, Bolt

Problem Description

Given a string s, determine whether it is a good string. A string is considered good if every character in the string has the same number of occurrences.

Key Insights

  • Use a hash table (or dictionary) to count the occurrence of each character.
  • After constructing the frequency map, verify if all values (counts) are identical.
  • Utilize a set to check the uniqueness of the frequency values; if the set size is 1, all characters occur equally.

Space and Time Complexity

Time Complexity: O(n) where n is the length of the string, since we traverse the string once to count the characters. Space Complexity: O(1) because the number of distinct characters is limited to 26 (lowercase English letters).

Solution

The solution involves iterating through the string, counting the frequency of each character using a hash table (or map). Once the counting is complete, we check if all frequency values are equal by converting them into a set. If the set's size is 1, it means all characters appear the same number of times. This is a direct and efficient O(n) solution in both time and space.

Code Solutions

# Function to check if all characters in the string have equal frequency
def are_occurrences_equal(s: str) -> bool:
    # Create a dictionary to count the occurrences of each character
    char_count = {}
    for char in s:
        # Increase the count for the current character
        char_count[char] = char_count.get(char, 0) + 1
    
    # Get all frequency values and check if they are all identical
    # Convert the list of counts to a set and verify it has only one unique value
    return len(set(char_count.values())) == 1

# Example usage:
s = "abacbc"
print(are_occurrences_equal(s))  # Should print True
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