#2243
Calculate Digit Sum of a String
pupil · 315 · lc easy +21 · verified · 67.7% accepted · 595 likes · top 74%
Description
You are given a digit string s and an integer k.
A processing round can occur when s has more than k characters. Each round:
- Split s into consecutive groups of k characters; the last group may be shorter.
- Replace each group with the string form of its digit sum. For example, "346" becomes "13".
- Concatenate all group results into the new s. If the new length still exceeds k, repeat.
Return s once it has at most k characters.
Example 1:
Input: s = "11111222223", k = 3
Output: "135"
Explanation:
- For the first round, we divide s into groups of size 3: "111", "112", "222", and "23".
Then we calculate the digit sum of each group: 1 + 1 + 1 = 3, 1 + 1 + 2 = 4, 2 + 2 + 2 = 6, and 2 + 3 = 5.
So, s becomes "3" + "4" + "6" + "5" = "3465" after the first round.
- For the second round, we divide s into "346" and "5".
Then we calculate the digit sum of each group: 3 + 4 + 6 = 13, 5 = 5.
So, s becomes "13" + "5" = "135" after second round.
Now, s.length <= k, so we return "135" as the answer.
Example 2:
Input: s = "00000000", k = 3
Output: "000"
Explanation:
We divide s into "000", "000", and "00".
Then we calculate the digit sum of each group: 0 + 0 + 0 = 0, 0 + 0 + 0 = 0, and 0 + 0 = 0.
s becomes "0" + "0" + "0" = "000", whose length is equal to k, so we return "000".
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