## DEV Community

Abhishek Chaudhary

Posted on

# Substrings of Size Three with Distinct Characters

A string is good if there are no repeated characters.

Given a string `s`​​​​​, return the number of good substrings of length three in `s`​​​​​​.

Note that if there are multiple occurrences of the same substring, every occurrence should be counted.

A substring is a contiguous sequence of characters in a string.

Example 1:

Input: s = "xyzzaz"
Output: 1
Explanation: There are 4 substrings of size 3: "xyz", "yzz", "zza", and "zaz".
The only good substring of length 3 is "xyz".

Example 2:

Input: s = "aababcabc"
Output: 4
Explanation: There are 7 substrings of size 3: "aab", "aba", "bab", "abc", "bca", "cab", and "abc".
The good substrings are "abc", "bca", "cab", and "abc".

Constraints:

• `1 <= s.length <= 100`
• `s`​​​​​​ consists of lowercase English letters.

SOLUTION:

``````class Solution:
def countGoodSubstrings(self, s: str) -> int:
n = len(s)
if n < 3:
return 0
dist = 0
ctr = [0] * 26
for i in range(3):
ctr[ord(s[i]) - ord('a')] += 1
for i in range(n - 3):
if max(ctr) == 1:
dist += 1
ctr[ord(s[i]) - ord('a')] -= 1
ctr[ord(s[i+3]) - ord('a')] += 1
if set(ctr) == {0, 1}:
dist += 1
return dist
``````