08. Shifting Letters.cpp

/*
Shifting Letters
================

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 <= 105
s consists of lowercase English letters.
shifts.length == s.length
0 <= shifts[i] <= 109
*/

class Solution {
public:
    string shiftingLetters(string s, vector<int> shifts) {
        shifts[shifts.size()-1] %= 26;
        
        for (int i = shifts.size()-2; i >= 0; --i) {
            shifts[i] = (shifts[i] % 26 + shifts[i+1] % 26) % 26;
        }
        
        for (int i = 0; i < s.size(); ++i) {
            int num = s[i] - 'a';
            num += shifts[i];
            num %= 26;
            s[i] = (num + 'a');
        }
        
        return s;
    }
};