LeetCode-in-Java

3271. Hash Divided String

Medium

You are given a string s of length n and an integer k, where n is a multiple of k. Your task is to hash the string s into a new string called result, which has a length of n / k.

First, divide s into n / k substrings, each with a length of k. Then, initialize result as an empty string.

For each substring in order from the beginning:

• The hash value of a character is the index of that character in the English alphabet (e.g., 'a' → 0, 'b' → 1, …, 'z' → 25).
• Calculate the sum of all the hash values of the characters in the substring.
• Find the remainder of this sum when divided by 26, which is called hashedChar.
• Identify the character in the English lowercase alphabet that corresponds to hashedChar.
• Append that character to the end of result.

Return result.

Example 1:

Input: s = “abcd”, k = 2

Output: “bf”

Explanation:

First substring: "ab", 0 + 1 = 1, 1 % 26 = 1, result[0] = 'b'.

Second substring: "cd", 2 + 3 = 5, 5 % 26 = 5, result[1] = 'f'.

Example 2:

Input: s = “mxz”, k = 3

Output: “i”

Explanation:

The only substring: "mxz", 12 + 23 + 25 = 60, 60 % 26 = 8, result[0] = 'i'.

Constraints:

• 1 <= k <= 100
• k <= s.length <= 1000
• s.length is divisible by k.
• s consists only of lowercase English letters.

Solution

public class Solution {
    public String stringHash(String s, int k) {
        var result = new StringBuilder();
        int i = 0;
        int sum = 0;
        while (i < s.length()) {
            sum += s.charAt(i) - 'a';
            if ((i + 1) % k == 0) {
                result.append((char) ('a' + sum % 26));
                sum = 0;
            }
            i++;
        }
        return result.toString();
    }
}

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