動機

prefix sum但是從後面來

Problem

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

Sol

class Solution:
    def shiftingLetters(self, s: str, shifts: List[int]) -> str:
        sums = shifts[::-1]
        for i in range(1,len(sums)):
            sums[i] += sums[i-1]
        sums = [x % 26 for x in sums[::-1]]
        #print(sums)
        return ''.join([chr(ord('a') + (ord(c) - ord('a') + i) % 26) for i,c in zip(sums, s)])