1945. Sum of Digits of String After Convert

Difficulty: Easy

Topics: String, Simulation

You are given a string s consisting of lowercase English letters, and an integer k.

First, convert s into an integer by replacing each letter with its position in the alphabet (i.e., replace 'a' with 1, 'b' with 2, ..., 'z' with 26). Then, transform the integer by replacing it with the sum of its digits. Repeat the transform operation k times in total.

For example, if s = "zbax" and k = 2, then the resulting integer would be 8 by the following operations:

Convert: "zbax" ➝ "(26)(2)(1)(24)" ➝ "262124" ➝ 262124
Transform #1: 262124 ➝ 2 + 6 + 2 + 1 + 2 + 4 ➝ 17
Transform #2: 17 ➝ 1 + 7 ➝ 8

Return the resulting integer after performing the operations described above.

Example 1:

Input: s = "iiii", k = 1
Output: 36
Explanation: The operations are as follows:
- Convert: "iiii" ➝ "(9)(9)(9)(9)" ➝ "9999" ➝ 9999
- Transform #1: 9999 ➝ 9 + 9 + 9 + 9 ➝ 36
- Thus the resulting integer is 36.

Example 2:

Input: s = "leetcode", k = 2
Output: 6
Explanation: The operations are as follows:
- Convert: "leetcode" ➝ "(12)(5)(5)(20)(3)(15)(4)(5)" ➝ "12552031545" ➝ 12552031545
- Transform #1: 12552031545 ➝ 1 + 2 + 5 + 5 + 2 + 0 + 3 + 1 + 5 + 4 + 5 ➝ 33
- Transform #2: 33 ➝ 3 + 3 ➝ 6
- Thus the resulting integer is 6.

Example 3:

Input: s = "zbax", k = 2
Output: 8

Constraints:

1 <= s.length <= 100
1 <= k <= 10
s consists of lowercase English letters.

Hint:

First, let's note that after the first transform the value will be at most 100 * 10 which is not much
After The first transform, we can just do the rest of the transforms by brute force

Solution:

We can break down the solution into two main steps:

Convert the string s into an integer:
- Each character in the string is replaced with its corresponding position in the alphabet (e.g., 'a' -> 1, 'b' -> 2, ..., 'z' -> 26).
- Concatenate all these numbers to form a large integer.
Transform the integer by summing its digits k times:
- For each transformation, sum all the digits of the current number.
- Repeat this transformation process k times.

Let's implement this solution in PHP: 1945. Sum of Digits of String After Convert

<?php
function getLucky($s, $k) {
    ...
    ...
    ...
    /**
     * go to ./solution.php
     */
}

// Test cases
echo getLucky("iiii", 1) . "\n"; // Output: 36
echo getLucky("leetcode", 2) . "\n"; // Output: 6
echo getLucky("zbax", 2) . "\n"; // Output: 8
?>

Explanation:

Convert the String:
- We loop through each character in the string s and calculate its corresponding alphabet position using ord($s[$i]) - ord('a') + 1.
- These values are concatenated to form a large string numStr representing the number.
Transform the Number:
- We loop k times, each time summing the digits of the current numStr.
- The result of this summing operation is stored back in numStr as a string to allow for further transformations.
- After k transformations, we return the final integer value.

Test Cases:

"iiii" with k = 1 converts to "9999", sums to 36, and since k=1, the final result is 36.
"leetcode" with k = 2 converts to "12552031545", sums to 33 in the first transform, and to 6 in the second transform, resulting in 6.
"zbax" with k = 2 converts to "262124", sums to 17 in the first transform, and to 8 in the second transform, resulting in 8.

This solution is efficient given the constraints and will work well within the provided limits.

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