159. Longest Substring with At Most Two Distinct Characters

 1 public class Solution {
 2     public int lengthOfLongestSubstringTwoDistinct(String s) {
 3         int[] array = new int[2];
 4         array[0] = -1;
 5         array[1] = -1;
 6         int max = 0;
 7         int start = 0;
 8         
 9         for (int i = 0; i < s.length(); i++) {
10             max = max > (i-start) ? max : (i-start); // i  is not included
11             char c = s.charAt(i);
12             if (array[0] == -1) {
13                 array[0] = c;
14             } else if (array[0] != c && array[1] == -1) { // in case array[1] = array[0] 
15                 array[1] = c;
16             } else if (array[0] != c && array[1] != c) {
17                 char pre = s.charAt(i-1);
18                 int j = i-2;
19                 while (j >= start && s.charAt(j) == pre) {
20                     j--;
21                 }
22                 j++;
23                 start = j;
24                 array[0] = pre;
25                 array[1] = c;
26             }
27         }
28         
29         max = max > (s.length() - start) ? max : (s.length() - start);
30         return max;
31     }
32 }