Score of a String - Video Solutions

Problem Overview: You are given a string s. The score of the string is the sum of the absolute differences between the ASCII values of every pair of adjacent characters. Iterate through the string, compare s[i] with s[i+1], compute abs(ord(s[i]) - ord(s[i+1])), and accumulate the result.

Approach 1: Iterative ASCII Difference Calculation (O(n) time, O(1) space)

The most direct solution scans the string once and compares each character with its neighbor. For each index i, compute the absolute difference between the ASCII values of s[i] and s[i+1]. Add this difference to a running total. Since each character is processed exactly once, the algorithm runs in O(n) time and uses O(1) extra space.

This approach relies on basic operations on a string: indexing and ASCII conversion. The key insight is that the score depends only on adjacent pairs, so no additional data structures are required. This makes it optimal for both runtime and memory usage. In practice, this is the implementation most developers use in interviews and production code because it is simple, readable, and efficient.

Approach 2: Recursive ASCII Difference Calculation (O(n) time, O(n) space)

The same logic can be expressed recursively. Define a recursive function that processes the first pair of characters, adds their ASCII difference, and then calls itself on the remainder of the string. Each call handles one adjacent pair and delegates the rest of the work to the next recursive step.

Although the algorithm still evaluates each pair exactly once (giving O(n) time complexity), recursion introduces a call stack that grows with the string length. This results in O(n) auxiliary space due to stack frames. The recursive style can help demonstrate understanding of recursion and problem decomposition, but it is less practical for very long strings compared to the iterative loop.

Both implementations depend on simple arithmetic operations and sequential traversal of a string. No sorting, hashing, or complex data structures are involved. The challenge mainly checks your understanding of ASCII values, absolute difference calculation, and careful iteration through adjacent elements.

Recommended for interviews: The iterative approach is the expected solution. Interviewers look for the ability to recognize that only adjacent characters matter and that a single pass through the string solves the problem in O(n) time with constant space. Implementing the recursive version can demonstrate deeper understanding, but the iterative method shows stronger practical judgment and efficiency.