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], , , , , . There are 4 groups with largest size.


Example 2:

Input: n = 2
Output: 2
Explanation: There are 2 groups ,  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;
}
}