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.

Similar: 3. Longest Substring Without Repeating Characters (Almost same !)

340. Longest Substring with At Most K Distinct Characters

239. Sliding Window Maximum

 

public class Solution {
    public int lengthOfLongestSubstringTwoDistinct(String s) {
        int[] array = new int[2];
        array[0] = -1;
        array[1] = -1;
        int max = 0;
        int start = 0;
        
        for (int i = 0; i < s.length(); i++) {
            max = max > (i-start) ? max : (i-start); // i  is not included
            char c = s.charAt(i);
            if (array[0] == -1) {
                array[0] = c;
            } else if (array[0] != c && array[1] == -1) { // in case array[1] = array[0] 
                array[1] = c;
            } else if (array[0] != c && array[1] != c) {
                char pre = s.charAt(i-1);
                int j = i-2;
                while (j >= start && s.charAt(j) == pre) {
                    j--;
                }
                j++;
                start = j;
                array[0] = pre;
                array[1] = c;
            }
        }
        
        max = max > (s.length() - start) ? max : (s.length() - start);
        return max;
    }
}