3838. Weighted Word Mapping

Time: O(total characters)

Space: O(1)

Intuition

Each word is mapped independently. Add the weight of every letter, reduce modulo 26, then convert that residue to a single output character using the reverse-alphabet formula 25 - sum. The only work per word is one pass over its characters plus constant-time modular arithmetic.

Algorithm

1Initialize an empty result string.
2For each word, set sum = 0.
3For each character c in the word, add weights[c - 'a'] to sum and take sum modulo 26.
4Append the character (char)('a' + (25 - sum)) to the result.
5Return the built string after all words are processed.

Example Walkthrough

Input: words = ["a", "b"], weights = [1,2,...,26]

1.For "a": sum = weights[0] = 1, so mapped index is 25 - 1 = 24 -> 'y'.
2.For "b": sum = weights[1] = 2, so mapped index is 25 - 2 = 23 -> 'x'.
3.Concatenate the mapped letters in input order.

Output: "yx"

Common Pitfalls

•Apply modulo 26 after every addition to keep the sum in range.
•The output index is 25 - sum, not sum itself.
•weights[i] corresponds to the i-th lowercase letter starting from 'a'.

3838.cs

// Approach: For each word, sum the per-letter weights modulo 26, then map that value to a
// character with index 25 - sum (equivalently the reverse-alphabet position).
// Time: O(total characters) Space: O(1) excluding output

public class Solution
{
    public string MapWordWeights(string[] words, int[] weights)
    {
        var ans = new StringBuilder();
        foreach (var w in words)
        {
            int s = 0;
            foreach (char c in w)
                s = (s + weights[c - 'a']) % 26;

            ans.Append((char)('a' + (25 - s)));
        }
        return ans.ToString();
    }
}

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