Leetcode 1742

The idea of this solution is pretty simple:

We use a map to store all the elements and their frequencies, and we use a variable called maximum to store the maximum frequency.
We loop from lowLimit to highLimit.
Inside the first loop, we make a nested loop to sum up all the digits of each number between lowLimit and highLimt.
After we have got the sum, we do m[sum]++ because we have to add one to the frequency of sum.
Then we check whether the new frequency is greater than our old maximum. If so, we should make maximum = m[sum].
Then we return maximum.

func countBalls(lowLimit int, highLimit int) int {
    m, maximum := make(map[int]int), 0
    for i := lowLimit; i <= highLimit; i++ {
        n, sum := i, 0

        for n > 0 {
            sum, n = sum+(n % 10), n / 10
        }
        m[sum]++

        if m[sum] > maximum {
            maximum = m[sum]
        }
    }
    return maximum
}

Using A max() Function:

func countBalls(lowLimit int, highLimit int) int {
    m, maximum := make(map[int]int), 0
    for i := lowLimit; i <= highLimit; i++ {
        n, sum := i, 0

        for n > 0 {
            sum, n = sum + (n % 10), n / 10
        }
        m[sum]++
        maximum = max(maximum, m[sum])
    }
    return maximum
}

func max(a, b int) int {
    if a > b {
        return a
    }
    return b
}