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1638. Count Substrings That Differ by One Character

Difficulty Topics

Description

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.

Solution

count-substrings-that-differ-by-one-character.py
class Solution:
    def countSubstrings(self, s: str, t: str) -> int:
        if s == t: return 0

        res = 0
        for i in range(len(s)):
            for z in range(i+1):
                c1 = s[i-z:i+1]
                l = len(c1)
                for j in range(len(t)-l+1):
                    c2 = t[j:j+l]
                    if c1 != c2 and len(c1) == len(c2) and sum(c1[i] != c2[i] for i in range(l)) == 1:
                        res += 1

        return res