1876. 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.

1876. Substrings of Size Three with Distinct Characters
``````struct Solution;

impl Solution {
fn count_good_substrings(s: String) -> i32 {
let s: Vec<char> = s.chars().collect();
let n = s.len();
let mut res = 0;
for i in 2..n {
if s[i] != s[i - 1] && s[i] != s[i - 2] && s[i - 1] != s[i - 2] {
res += 1;
}
}
res
}
}

#[test]
fn test() {
let s = "xyzzaz".to_string();
let res = 1;
assert_eq!(Solution::count_good_substrings(s), res);
let s = "aababcabc".to_string();
let res = 4;
assert_eq!(Solution::count_good_substrings(s), res);
}
``````