LeetCode 1399: Count Largest Group Solution

Master LeetCode problem 1399 (Count Largest Group), a easy 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.

1399. Count Largest Group

Easy

Hash Table Math

Problem Explanation

Explanation

To solve this problem, we iterate from 1 to n, calculate the sum of digits for each number, and keep track of the frequency of each sum. Then, we find the maximum frequency to determine the number of groups with the largest size.

Create a frequency map to store the sum of digits and their frequencies.
Iterate from 1 to n, calculate the sum of digits for each number.
Update the frequency map with the sum of digits.
Find the maximum frequency in the frequency map.
Count the number of groups with the largest size (having the maximum frequency).

Time Complexity: O(n log n) due to calculating sum of digits for each number up to n. Space Complexity: O(n) for the frequency map.

Solution Code

class Solution {
    public int countLargestGroup(int n) {
        Map<Integer, Integer> freqMap = new HashMap<>();
        int maxFreq = 0;

        for (int i = 1; i <= n; i++) {
            int sum = 0;
            int num = i;
            while (num > 0) {
                sum += num % 10;
                num /= 10;
            }
            int freq = freqMap.getOrDefault(sum, 0) + 1;
            freqMap.put(sum, freq);
            maxFreq = Math.max(maxFreq, freq);
        }

        int count = 0;
        for (int freq : freqMap.values()) {
            if (freq == maxFreq) {
                count++;
            }
        }

        return count;
    }
}

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