159. Longest Substring with At Most Two Distinct Characters

LengthOfLongestSubstringTwoDistinct.cs

public class Solution {
  public int LengthOfLongestSubstringTwoDistinct(string s) {
    var i = 0;
    var longest = 0;
    var n= s.Length;
    while(i < n){
      var start = i;
      var firstDistinct = s[i];
      while(i + 1 < n && s[i + 1] == firstDistinct)
        i++;
      
      if(i + 1 < n){
        i++;
        var secondDistinct = s[i];
        while(i + 1 < n && (s[i + 1] == firstDistinct || s[i + 1] == secondDistinct))
          i++;
        longest = Math.Max(longest, i - start + 1);
        var lastDistinctChar = s[i];
        while(i - 1 >= 0 && s[i - 1] == lastDistinctChar)
          i--;
      }
      else{
        longest = Math.Max(longest, i - start + 1);
        i++;
      }
    }
    return longest;
  }
}