4056 Longest Balanced Substring Ii
Longest Balanced Substring II 
You are given a string s consisting only of the characters ‘a’, ‘b’, and ‘c’.
A substring of s is called balanced if all distinct characters in the substring appear the same number of times.
Return the length of the longest balanced substring of s.
Example 1:
Input: s = “abbac”
Output: 4
Explanation:
The longest balanced substring is “abba” because both distinct characters ‘a’ and ‘b’ each appear exactly 2 times.
Example 2:
Input: s = “aabcc”
Output: 3
Explanation:
The longest balanced substring is “abc” because all distinct characters ‘a’, ‘b’ and ‘c’ each appear exactly 1 time.
Example 3:
Input: s = “aba”
Output: 2
Explanation:
One of the longest balanced substrings is “ab” because both distinct characters ‘a’ and ‘b’ each appear exactly 1 time. Another longest balanced substring is “ba”.
Constraints:
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1 <= s.length <= 105
s contains only the characters 'a', 'b', and 'c'.
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class Solution:
def longestBalanced(self, S: str) -> int:
N = len(S)
P = [[0, 0, 0]]
for c in S:
P.append(P[-1][:])
P[-1]["abc".index(c)] += 1
ans = 0
first = {}
for i, (a, b, c) in enumerate(P):
for key in [
("abc", a - b, a - c),
("ab", a - b, c),
("bc", b - c, a),
("ca", c - a, b),
("a", b, c),
("b", c, a),
("c", a, b),
]:
ans = max(ans, i - first.get(key, i))
first.setdefault(key, i)
return ans