Longest Substring with At Most K Distinct Characters.java

    public int lengthOfLongestSubStringKDistinct(String s) {
        int n = s.length();
        int[] count = new int[256];
        int i = 0, numDistinct = 0, ans = 0;

        for (int j = 1; j < s.length(); j++) {
            if (count[s.charAt(j)] == 0) {
                numDistinct++;
            }
            count[s.charAt(j)]++;
            while (numDistinct > 2) {
                count[s.charAt(i)]--;
                if (count[s.charAt(i)] == 0) {
                    numDistinct--;
                }
                i++;
            }
            ans = Math.max(ans, j - i + 1);
        }
        return ans;
    }