The hash of a 0-indexed string `s` of length `k`, given integers `p` and `m`, is computed using the following function:

- `hash(s, p, m) = (val(s[0]) * p0 + val(s[1]) * p1 + ... + val(s[k-1]) * pk-1) mod m`.

Where `val(s[i])` represents the index of `s[i]` in the alphabet from `val('a') = 1` to `val('z') = 26`.

You are given a string `s` and the integers `power`, `modulo`, `k`, and `hashValue.` Return `sub`, the first substring of `s` of length `k` such that `hash(sub, power, modulo) == hashValue`.

The test cases will be generated such that an answer always exists.

A substring is a contiguous non-empty sequence of characters within a string.

Example 1:

    Input: s = "leetcode", power = 7, modulo = 20, k = 2, hashValue = 0
    Output: "ee"
    Explanation: The hash of "ee" can be computed to be hash("ee", 7, 20) = (5 * 1 + 5 * 7) mod 20 = 40 mod 20 = 0.
    "ee" is the first substring of length 2 with hashValue 0. Hence, we return "ee".

Example 2:

    Input: s = "fbxzaad", power = 31, modulo = 100, k = 3, hashValue = 32
    Output: "fbx"
    Explanation: The hash of "fbx" can be computed to be hash("fbx", 31, 100) = (6 * 1 + 2 * 31 + 24 * 312) mod 100 = 23132 mod 100 = 32.
    The hash of "bxz" can be computed to be hash("bxz", 31, 100) = (2 * 1 + 24 * 31 + 26 * 312) mod 100 = 25732 mod 100 = 32.
    "fbx" is the first substring of length 3 with hashValue 32. Hence, we return "fbx".
    Note that "bxz" also has a hash of 32 but it appears later than "fbx".

Constraints:

- `1 <= k <= s.length <= 2 * 104`
- `1 <= power, modulo <= 109`
- `0 <= hashValue < modulo`
- `s` consists of lowercase English letters only.
- The test cases are generated such that an answer always exists.