Longest Substring With At Most K Distinct Characters

Given a string, find the length of the longest substring T that contains at most k distinct characters.

For example, Given s = “eceba” and k = 2,

T is "ece" which its length is 3.

Analyses: Map each character in the string into a index in an array times, size of that array is from ASCII size. During the process of scanning, update the frequencies of each character. Have a variable count to label how many different characters occur. Whenever the count exceeds k, we know that shorten our range: Let the left pointer move right until the frequency of the character pointed by left is 1. 

public class Solution {
    public int lengthOfLongestSubstringKDistinct(String s, int k) {
        int result = 0, left = 0, n = s.length(), count = 0;
        int[] times = new int[256]; // map char in s to a index
        for (int right = 0; right < n; right++) {
            if (times[s.charAt(right)]++ == 0) count++;
            
            if (count > k) {
                while (--times[s.charAt(left++)] > 0);
                count--;
            }
            
            result = Math.max(result, right - left + 1);
        }
        return result;
    }
}