LeetCode 1638: Count Substrings That Differ by One Character Solution

Master LeetCode problem 1638 (Count Substrings That Differ by One Character), a medium challenge, with our optimized solutions in Java, C++, and Python. Explore detailed explanations, test your code in our interactive editor, and prepare for coding interviews.

1638. Count Substrings That Differ by One Character

Medium

Hash Table String Dynamic Programming Enumeration

Problem Explanation

Explanation

To solve this problem, we can iterate through all possible substrings of string s and string t. For each pair of substrings, we check if they differ by exactly one character. To efficiently check this, we compare the substrings character by character and keep track of the number of differences encountered. If the number of differences is exactly one, we increment the count of valid substrings. The time complexity of this approach is O(n^4) where n is the length of the strings s and t.

Solution Code

class Solution {
    public int countSubstrings(String s, String t) {
        int count = 0;
        for (int i = 1; i <= s.length(); i++) {
            for (int j = 0; j < s.length() - i + 1; j++) {
                String subS = s.substring(j, j + i);
                for (int k = 1; k <= t.length(); k++) {
                    for (int l = 0; l < t.length() - k + 1; l++) {
                        String subT = t.substring(l, l + k);
                        if (checkDifferByOne(subS, subT)) {
                            count++;
                        }
                    }
                }
            }
        }
        return count;
    }
    
    private boolean checkDifferByOne(String s, String t) {
        int diffCount = 0;
        for (int i = 0; i < s.length(); i++) {
            if (s.charAt(i) != t.charAt(i)) {
                diffCount++;
                if (diffCount > 1) {
                    return false;
                }
            }
        }
        return diffCount == 1;
    }
}

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