Is Shifting Letters easy or hard?

Shifting Letters is considered a medium-level problem. The main difficulty comes from recognizing that each shift affects all earlier characters. Once you realize the overlapping operations can be combined using cumulative sums, the implementation becomes straightforward.

Shifting Letters Python/Java solution

In Python or Java, the optimal implementation iterates from the end of the string while accumulating shift values modulo 26. Convert characters to numeric offsets using 'a', apply the shift, then convert back to characters. Both languages achieve O(n) time complexity with constant extra space.

How to solve Shifting Letters in O(n)?

Compute the cumulative shift while traversing from right to left. Maintain a variable runningShift and update it as runningShift = (runningShift + shifts[i]) % 26. Apply that shift to s[i] using modular arithmetic. This avoids repeated updates and transforms the problem into a single linear pass.

What is the best approach for Shifting Letters?

The optimized backward cumulative shift approach is the best solution. Traverse the string from right to left while maintaining a running shift value. Each step adds shifts[i] to the running total and applies it modulo 26 to the character. This processes every character once with O(n) time and O(1) extra space.

Is Shifting Letters asked at Google/Amazon/Meta?

Shifting Letters represents a common interview pattern involving prefix sums and string manipulation. Variations of cumulative operations on arrays or strings appear frequently in interviews at companies like Amazon, Google, and Meta, especially in medium-level coding rounds.

What data structure is used in Shifting Letters?

The problem primarily uses arrays and strings along with prefix-sum style cumulative calculations. No advanced data structures are required. Efficient solutions rely on modular arithmetic and maintaining a running suffix sum while iterating through the array.

What is the time complexity of Shifting Letters?

The optimal solution runs in O(n) time where n is the length of the string. Each character is visited exactly once while accumulating the shift values. The naive simulation approach takes O(n^2) because each shift operation repeatedly modifies earlier characters.

Description Solution Video 4:54

848. Shifting Letters

Medium46.1% acceptance3 companies

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

Asked at 3 companies

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Google Bloomberg

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848. Shifting Letters

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