848. Shifting Letters 

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class Solution {
    public String shiftingLetters(String s, int[] shifts) {
        int shiftCount = 0;
        char[] chars = s.toCharArray();
        for (int i = chars.length - 1; i >= 0; i--) {
            shiftCount += shifts[i] % 26;
            chars[i] = (char) ('a' + (chars[i] - 'a' + shiftCount) % 26);
        }
        return new String(chars);
    }
}

References

848. Shifting Letters