#3498

Easy

LeetCode Problem Workspace

Reverse Degree of a String

Calculate the reverse degree of a string by simulating operations on its characters based on their positions in the alphabet.

string simulation

Problem Statement

Given a string s, you are tasked with calculating its reverse degree. The reverse degree is determined by applying an operation to each character of the string, which is based on its position in the alphabet.

For each character in the string, calculate its position in the reverse alphabet (starting from 'z' = 1, 'y' = 2, ..., 'a' = 26). Sum these positions to return the reverse degree of the string.

Examples

Example 1

Input: s = "abc"

Output: 148

The reversed degree is 26 + 50 + 72 = 148 .

Example 2

Input: s = "zaza"

Output: 160

The reverse degree is 1 + 52 + 3 + 104 = 160 .

Constraints

1 <= s.length <= 1000
s contains only lowercase English letters.

Solution Approach

Simulate Character Operations

Start by simulating the reverse alphabet position for each character in the string. For every character, find its reverse alphabet position and accumulate the sum.

Efficient Accumulation

Instead of re-calculating positions repeatedly, directly map each character to its reverse position using its ASCII value, making the summing process efficient.

Edge Case Considerations

Handle edge cases where the string length is minimal or maximal. Ensure that operations scale appropriately for strings of size up to 1000 characters.

Complexity Analysis

Metric	Value
Time	Depends on the final approach
Space	Depends on the final approach

The time complexity depends on the approach used to traverse the string and compute the reverse alphabet positions. A direct calculation of each character's reverse degree gives a time complexity of O(n), where n is the length of the string. The space complexity depends on whether any additional data structures are used, but with a direct approach, the space complexity is O(1).

What Interviewers Usually Probe

Ensure the candidate correctly simulates the reverse position of each character.
Watch for an efficient solution that avoids unnecessary recalculations.
Look for proper handling of edge cases like strings of minimal and maximal length.

Common Pitfalls or Variants

Common pitfalls

Misunderstanding the reverse alphabet positioning, leading to incorrect calculations.
Recalculating character positions multiple times rather than storing values for efficiency.
Forgetting to properly handle the string length limits and failing to optimize for larger inputs.

Follow-up variants

Consider extending the problem to handle mixed-case strings and their reverse degree.
Change the problem to calculate the forward degree and compare the solutions.
Challenge the candidate to optimize the solution further with a different approach, like using precomputed values.

FAQ

What is the reverse degree of a string?

The reverse degree of a string is the sum of the reverse positions of each character in the string, where 'z' = 1, 'y' = 2, ..., 'a' = 26.

How do I simulate the reverse alphabet position for each character?

For each character, find its ASCII value and subtract it from the ASCII value of 'z' to get the reverse alphabet position.

How can I optimize the solution for large strings?

You can optimize the solution by calculating each character's reverse position once and summing them directly, without redundant operations.

What is the complexity of the reverse degree problem?

The time complexity is O(n), where n is the length of the string. The space complexity is O(1) if no additional data structures are used.

How does GhostInterview help with the reverse degree of a string problem?

GhostInterview provides efficient techniques, helps with simulating character operations, and ensures proper handling of edge cases for calculating the reverse degree.

terminal

Solution

Solution 1: Simulation

We can simulate the reverse degree of each character in the string. For each character, calculate its position in the reverse alphabet, multiply it by its position in the string, and then sum up all the results.

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class Solution:
    def reverseDegree(self, s: str) -> int:
        ans = 0
        for i, c in enumerate(s, 1):
            x = 26 - (ord(c) - ord("a"))
            ans += i * x
        return ans

Continue Practicing

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