LeetCode Longest Substring with At Most Two Distinct Characters

原题链接在这里：https://leetcode.com/problems/longest-substring-with-at-most-two-distinct-characters/

题目：

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.

题解：

与Longest Substring Without Repeating Characters类似。快慢指针维护substring的方法在Minimum Window Substring里有总结.

runner 扫过 char的frequency加一. 条件count++.

当count > 2后移动walker直到count减到2

Time Complexity: O(n), 窗口只移动一遍. Space: O(1). map size.

AC Java:

 public class Solution {
     public int lengthOfLongestSubstringTwoDistinct(String s) {
         int res = 0;
         int [] map = new int[256];
         int walker = 0;
         int runner = 0;
         int count = 0;
         while(runner < s.length()){
             if(map[s.charAt(runner++)]++ == 0){
                 count++;
             }
             while(count > 2){
                 if(map[s.charAt(walker++)]-- == 1){
                     count--;
                 }
             }
             res = Math.max(res, runner - walker);
         }
         return res;
     }
 }

类似Longest Substring with At Most K Distinct Characters, Fruit Into Baskets, Max Consecutive Ones II.