code javascript: Find a string of a given length containing as many different lower$-$case letters as possible, in which each letter occurs an equal number of times.

Task description

Write a function solution that, given an integer N$,$ returns a string of length N containing as many different lower$-$case letters $(\text{'}$a$\text{'}-\text{'}$z$\text{'})$ as possible, in which each letter occurs an equal number of times.

Examples:

$1.$ Given N $=3,$ the function may return "fig", "pea", "nut", etc. Each of these strings contains three different letters with the same number of occurrences.

$2.$ Given N $=5,$ the function may return "mango", "grape", "melon", etc.

$3.$ Given N $=30,$ the function may return "aabbcc...oo$"($each letter from $\text{'}$a$\text{'}$ to $\text{'}$o$\text{'}$ occurs twice$).$ The string contains $15$ different letters.

Write an efficient algorithm for the following assumptions:

$$ N is an integer within the range $[1.\mathrm{.}200,000].$