159. Longest Substring with At Most Two Distinct Characters

159.java

class Solution {
    public int lengthOfLongestSubstringTwoDistinct(String s) {
        int ans = 0;
        int left = 0;
        Map<Character, Integer> freq = new HashMap<>();
        for(int right = 0; right < s.length(); right++) {
            char c = s.charAt(right);
            freq.put(c, freq.getOrDefault(c, 0) + 1);

            while(freq.size() > 2) {
                char lc = s.charAt(left);
                freq.put(lc, freq.get(lc) - 1);
                if(freq.get(lc) == 0)
                    freq.remove(lc);
                left++;
            }

            ans = Math.max(ans, right - left + 1);
        }

        return ans;
    }
}