2381. Shifting Letters II

Description

You are given a string s of lowercase English letters and a 2D integer array shifts where shifts[i] = [starti, endi, directioni]. For every i, shift the characters in s from the index starti to the index endi (inclusive) forward if directioni = 1, or shift the characters backward if directioni = 0.

Shifting a character forward means replacing it with the next letter in the alphabet (wrapping around so that 'z' becomes 'a'). Similarly, shifting a character backward means replacing it with the previous letter in the alphabet (wrapping around so that 'a' becomes 'z').

Return the final string after all such shifts to s are applied.

 

Example 1:

Input: s = "abc", shifts = [[0,1,0],[1,2,1],[0,2,1]]
Output: "ace"
Explanation: Firstly, shift the characters from index 0 to index 1 backward. Now s = "zac".
Secondly, shift the characters from index 1 to index 2 forward. Now s = "zbd".
Finally, shift the characters from index 0 to index 2 forward. Now s = "ace".

Example 2:

Input: s = "dztz", shifts = [[0,0,0],[1,1,1]]
Output: "catz"
Explanation: Firstly, shift the characters from index 0 to index 0 backward. Now s = "cztz".
Finally, shift the characters from index 1 to index 1 forward. Now s = "catz".

 

Constraints:

• 1 <= s.length, shifts.length <= 5 * 104
• shifts[i].length == 3
• 0 <= starti <= endi < s.length
• 0 <= directioni <= 1
• s consists of lowercase English letters.

Solution

shifting-letters-ii.py

class Solution:
    def shiftingLetters(self, s: str, shifts: List[List[int]]) -> str:
        n = len(s)
        A = [ord(x) - ord('a') for x in s]
        B = [0] * (n + 1)

        for start, end, direction in shifts:
            c = 1 if direction == 1 else -1

            B[start] += c
            B[end + 1] -= c

        for i in range(1, len(B)):
            B[i] += B[i - 1]

        for index, (a, b) in enumerate(zip(A, B)):
            A[index] += b
            A[index] %= 26

        return "".join([chr(x + ord("a")) for x in A])