LeetCode 2168: Unique Substrings With Equal Digit Frequency Solution

Master LeetCode problem 2168 (Unique Substrings With Equal Digit Frequency), a medium challenge, with our optimized solutions in Java, C++, and Python. Explore detailed explanations, test your code in our interactive editor, and prepare for coding interviews.

2168. Unique Substrings With Equal Digit Frequency

Medium

Hash Table String Rolling Hash Counting Hash Function

Problem Explanation

Explanation

To solve this problem, we can iterate through all substrings of the given string and calculate the frequency of each digit in each substring. We then check if the frequencies of digits in the substring are equal. If they are equal, we increment the count of unique substrings with equal digit frequencies. We can use a hashmap to store the frequency of digits in each substring.

Algorithm:

Initialize a count variable to 0 to store the count of unique substrings with equal digit frequencies.
Iterate through all substrings of the given string.
For each substring, calculate the frequency of each digit using a hashmap.
Check if the frequencies of digits in the substring are equal. If they are equal, increment the count.
Return the count of unique substrings with equal digit frequencies.

Time Complexity: O(n^2 * m) where n is the length of the input string and m is the maximum number of unique digits in a substring.

Space Complexity: O(m) where m is the maximum number of unique digits in a substring.

Solution Code

class Solution {
    public int uniqueSubstringsWithEqualDigitFrequency(String s) {
        int count = 0;
        for (int i = 0; i < s.length(); i++) {
            for (int j = i + 1; j <= s.length(); j++) {
                String sub = s.substring(i, j);
                Map<Character, Integer> freq = new HashMap<>();
                for (char c : sub.toCharArray()) {
                    freq.put(c, freq.getOrDefault(c, 0) + 1);
                }
                if (checkEqualFrequency(freq)) {
                    count++;
                }
            }
        }
        return count;
    }
    
    private boolean checkEqualFrequency(Map<Character, Integer> freq) {
        Set<Integer> set = new HashSet<>(freq.values());
        return set.size() == 1;
    }
}

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