Question

2243. Calculate Digit Sum of a String

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Description

You are given a string s consisting of digits and an integer k.

A round can be completed if the length of s is greater than k. In one round, do the following:

1. Divide s into consecutive groups of size k such that the first k characters are in the first group, the next k characters are in the second group, and so on. Note that the size of the last group can be smaller than k.
2. Replace each group of s with a string representing the sum of all its digits. For example, "346" is replaced with "13" because 3 + 4 + 6 = 13.
3. Merge consecutive groups together to form a new string. If the length of the string is greater than k, repeat from step 1.

Return s _after all rounds have been completed_.

 

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".

 

Constraints:

• 1 <= s.length <= 100
• 2 <= k <= 100
• s consists of digits only.

Solutions

Solution 1

class Solution:
  def digitSum(self, s: str, k: int) -> str:
    while len(s) > k:
      t = []
      n = len(s)
      for i in range(0, n, k):
        x = 0
        for j in range(i, min(i + k, n)):
          x += int(s[j])
        t.append(str(x))
      s = "".join(t)
    return s

class Solution {
  public String digitSum(String s, int k) {
    while (s.length() > k) {
      int n = s.length();
      StringBuilder t = new StringBuilder();
      for (int i = 0; i < n; i += k) {
        int x = 0;
        for (int j = i; j < Math.min(i + k, n); ++j) {
          x += s.charAt(j) - '0';
        }
        t.append(x);
      }
      s = t.toString();
    }
    return s;
  }
}

class Solution {
public:
  string digitSum(string s, int k) {
    while (s.size() > k) {
      string t;
      int n = s.size();
      for (int i = 0; i < n; i += k) {
        int x = 0;
        for (int j = i; j < min(i + k, n); ++j) {
          x += s[j] - '0';
        }
        t += to_string(x);
      }
      s = t;
    }
    return s;
  }
};

func digitSum(s string, k int) string {
  for len(s) > k {
    t := &strings.Builder{}
    n := len(s)
    for i := 0; i < n; i += k {
      x := 0
      for j := i; j < i+k && j < n; j++ {
        x += int(s[j] - '0')
      }
      t.WriteString(strconv.Itoa(x))
    }
    s = t.String()
  }
  return s
}

function digitSum(s: string, k: number): string {
  let ans = [];
  while (s.length > k) {
    for (let i = 0; i < s.length; i += k) {
      let cur = s.slice(i, i + k);
      ans.push(cur.split('').reduce((a, c) => a + parseInt(c), 0));
    }
    s = ans.join('');
    ans = [];
  }
  return s;
}

Solution 2

class Solution:
  def digitSum(self, s: str, k: int) -> str:
    if len(s) <= k:
      return s
    t = []
    while s:
      t.append(str(sum(int(v) for v in s[:k])))
      s = s[k:]
    return self.digitSum(''.join(t), k)