main.go

// Source: https://leetcode.com/problems/shifting-letters
// Title: Shifting Letters
// Difficulty: Medium
// Author: Mu Yang <http://muyang.pro>

////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
// You are given a string `s` of lowercase English letters and an integer array `shifts` of the same length.
//
// Call the `shift()` of a letter, the next letter in the alphabet, (wrapping around so that `'z'` becomes `'a'`).
//
// - For example, `shift('a') = 'b'`, `shift('t') = 'u'`, and `shift('z') = 'a'`.
//
// Now for each `shifts[i] = x`, we want to shift the first `i + 1` letters of `s`, `x` times.
//
// Return the final string after all such shifts to s are applied.
//
// **Example 1:**
//
// ```
// Input: s = "abc", shifts = [3,5,9]
// Output: "rpl"
// Explanation: We start with "abc".
// After shifting the first 1 letters of s by 3, we have "dbc".
// After shifting the first 2 letters of s by 5, we have "igc".
// After shifting the first 3 letters of s by 9, we have "rpl", the answer.
// ```
//
// **Example 2:**
//
// ```
// Input: s = "aaa", shifts = [1,2,3]
// Output: "gfd"
// ```
//
// **Constraints:**
//
// - `1 <= s.length <= 10^5`
// - `s` consists of lowercase English letters.
// - `shifts.length == s.length`
// - `0 <= shifts[i] <= 10^9`
//
////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////

package main

func shiftingLetters(s string, shifts []int) string {
	n := len(s)
	bytes := []byte(s)

	move := 0
	for i := n - 1; i >= 0; i-- {
		move += shifts[i]
		bytes[i] = byte(_mod(int(bytes[i]-'a')+move, 26)) + 'a'
	}

	return string(bytes)
}

func _mod(a, b int) int {
	a %= b
	if a < 0 {
		a += b
	}
	return a
}