Given an integer k and a string s, find the length of the longest substring that contains at most k distinct characters. For example, given s = "abcba" and k = 2, the longest substring with k distinct characters is "bcb".

daily-coding-problem-13.rb

#!/usr/bin/env ruby
require 'set'

def distinct_char(s,k)
    #assert(len(s) >= k)

    start_idx, end_idx, max_length = 0, k, k
    while end_idx < s.length do
        end_idx += 1
        while true do
            distinct_chars = s[start_idx,end_idx].split(//).to_set().length
            if distinct_chars <= k 
                break 
            end 
            start_idx += 1
        end
        max_length = [max_length, end_idx - start_idx].max
    end
    return max_length
end 

if __FILE__ == $0
    s = "aabbcc"
    k = 2
    puts distinct_char(s,k)
end