Formatted question description: https://leetcode.ca/all/1399.html

1399. Count Largest Group (Easy)

Given an integer n. Each number from 1 to n is grouped according to the sum of its digits. 

Return how many groups have the largest size.

 

Example 1:

Input: n = 13
Output: 4
Explanation: There are 9 groups in total, they are grouped according sum of its digits of numbers from 1 to 13:
[1,10], [2,11], [3,12], [4,13], [5], [6], [7], [8], [9]. There are 4 groups with largest size.

Example 2:

Input: n = 2
Output: 2
Explanation: There are 2 groups [1], [2] of size 1.

Example 3:

Input: n = 15
Output: 6

Example 4:

Input: n = 24
Output: 5

 

Constraints:

  • 1 <= n <= 10^4

Related Topics:
Array

Solution 1.

// OJ: https://leetcode.com/problems/count-largest-group/

// Time: O(N)
// Space: O(N)
class Solution {
public:
    int countLargestGroup(int n) {
        unordered_map<int, int> m;
        for (int i = 1; i <= n; ++i) {
            int sum = 0, x = i;
            while (x) {
                sum += x % 10;
                x /= 10;
            }
            m[sum]++;
        }
        int maxSize = 0;
        for (auto &p : m) {
            maxSize = max(maxSize, p.second);
        }
        int ans = 0;
        for (auto &p : m) {
            if (p.second == maxSize) ++ans;
        }
        return ans;
    }
};

Java

class Solution {
    public int countLargestGroup(int n) {
        int maxCount = 0;
        Map<Integer, Integer> map = new HashMap<Integer, Integer>();
        for (int i = 1; i <= n; i++) {
            int sum = sumDigits(i);
            int count = map.getOrDefault(sum, 0) + 1;
            map.put(sum, count);
            maxCount = Math.max(maxCount, count);
        }
        int groups = 0;
        Set<Integer> keySet = map.keySet();
        for (int key : keySet) {
            if (map.get(key) == maxCount)
                groups++;
        }
        return groups;
    }

    public int sumDigits(int num) {
        char[] array = String.valueOf(num).toCharArray();
        int sum = 0;
        for (char c : array)
            sum += c - '0';
        return sum;
    }
}

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