LeetCode 2156: Find Substring With Given Hash Value Solution

Master LeetCode problem 2156 (Find Substring With Given Hash Value), a hard 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.

2156. Find Substring With Given Hash Value

Hard

String Sliding Window Rolling Hash Hash Function

Problem Explanation

Explanation:

To solve this problem, we will iterate through all possible substrings of length k in the input string s. For each substring, we will calculate its hash value using the provided hash function and compare it with the given hashValue. If we find a match, we return that substring.

Here are the steps:

Iterate through all substrings of length k in the input string s.
For each substring, calculate its hash value using the given hash function.
Compare the calculated hash value with the given hashValue.
If they match, return that substring.

The time complexity of this solution is O(n * k), where n is the length of the input string s and k is the length of the substring we are searching for. The space complexity is O(1) as we are not using any extra space other than some variables.

Solution Code

class Solution {
    public String findSubstring(String s, int power, int modulo, int k, int hashValue) {
        for (int i = 0; i <= s.length() - k; i++) {
            String sub = s.substring(i, i + k);
            if (calculateHash(sub, power, modulo) == hashValue) {
                return sub;
            }
        }
        return "";
    }
    
    private int calculateHash(String s, int power, int modulo) {
        int hash = 0;
        for (int i = 0; i < s.length(); i++) {
            hash = (hash * power + (s.charAt(i) - 'a' + 1)) % modulo;
        }
        return hash;
    }
}

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