lc159-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.

class Solution {
public:
    int lengthOfLongestSubstringTwoDistinct(string s) {
        int hash[128] = {0};
        int l = s.length();
        int max_len=0, cur_nchar=0;
        for (int i=0, j=0; i<l; i++) {
            if (!hash[s[i]-'A']++) cur_nchar++;
            if (cur_nchar <= 2) max_len = max(max_len, i-j+1);
            while (cur_nchar > 2) {
                if(!--hash[s[j++]-'A']) cur_nchar--;
            }
        }
        return max_len;
    }
};