159. Longest Substring With at Most Two Distinct Characters

Given a string, find the length of the longest substring T that contains at most 2 distinct characters.

For example, Given s = “eceba”,

T is “ece” which its length is 3.

Same solution as K distinct characters

Can use two variables to track the last index of the characters

public class Solution {
    public int lengthOfLongestSubstringTwoDistinct(String s) {
        if (s == null || s.length() == 0) {
            return 0;
        }
        int max = 0, left = 0;
        HashMap<Character, Integer> map = new HashMap<>();
        for (int i = 0; i < s.length(); i++) {
            char cur = s.charAt(i);
            map.put(cur, map.getOrDefault(cur, 0) + 1);
            while (map.size() > 2) {
                char leftChar = s.charAt(left);
                if (map.containsKey(leftChar)) {
                    map.put(leftChar, map.get(leftChar) - 1);
                    if (map.get(leftChar) == 0) {
                        map.remove(leftChar);
                    }
                }
                left++;
            }
            max = Math.max(max, i - left + 1);
        }
        return max;
    }
}