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1638. Count Substrings That Differ by One Character

Given two strings s and t, find the number of ways you can choose a non-empty substring of s and replace a single character by a different character such that the resulting substring is a substring of t. In other words, find the number of substrings in s that differ from some substring in t by exactly one character.

For example, the underlined substrings in "computer" and "computation" only differ by the 'e'/'a', so this is a valid way.

Return the number of substrings that satisfy the condition above.

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

Example 1:

Input: s = "aba", t = "baba"
Output: 6
Explanation: The following are the pairs of substrings from s and t that differ by exactly 1 character:
("aba", "baba")
("aba", "baba")
("aba", "baba")
("aba", "baba")
("aba", "baba")
("aba", "baba")
The underlined portions are the substrings that are chosen from s and t.

Example 2:

Input: s = "ab", t = "bb"
Output: 3
Explanation: The following are the pairs of substrings from s and t that differ by 1 character:
("ab", "bb")
("ab", "bb")
("ab", "bb")
The underlined portions are the substrings that are chosen from s and t.

Constraints:

• 1 <= s.length, t.length <= 100
• s and t consist of lowercase English letters only.

Solutions (Rust)

1. Solution

impl Solution {
    pub fn count_substrings(s: String, t: String) -> i32 {
        let s = s.as_bytes();
        let t = t.as_bytes();
        let mut ret = 0;

        for i in 0..s.len() {
            for j in 0..t.len() {
                let mut count = 0;

                for k in 0..(s.len() - i).min(t.len() - j) {
                    if s[i + k] != t[j + k] {
                        count += 1;
                    }
                    if count > 1 {
                        break;
                    } else if count == 1 {
                        ret += 1;
                    }
                }
            }
        }

        ret
    }
}