3271. Hash Divided String

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.

class Solution {
public:
    string stringHash(string s, int k) {
        int n = s.length();
        vector<char> sums(n/k);
        for(int i = 0; i < n; i++) sums[i/k] = (sums[i/k] + s[i] - 'a') % 26;
        string res = "";
        for(int i = 0; i < n / k; i++) res.push_back(sums[i] % 26 + 'a');
        return res;
    }
};