3463. Check If Digits Are Equal in String After Operations II - Solution & Explanation

You are given a string s consisting of digits. Perform the following operation repeatedly until the string has exactly two digits:

For each pair of consecutive digits in s, starting from the first digit, calculate a new digit as the sum of the two digits modulo 10.
Replace s with the sequence of newly calculated digits, maintaining the order in which they are computed.

Return true if the final two digits in s are the same; otherwise, return false.

Example 1:

Input: s = "3902"

Output: true

Explanation:

Initially, s = "3902"
First operation:
- (s[0] + s[1]) % 10 = (3 + 9) % 10 = 2
- (s[1] + s[2]) % 10 = (9 + 0) % 10 = 9
- (s[2] + s[3]) % 10 = (0 + 2) % 10 = 2
- s becomes "292"
Second operation:
- (s[0] + s[1]) % 10 = (2 + 9) % 10 = 1
- (s[1] + s[2]) % 10 = (9 + 2) % 10 = 1
- s becomes "11"
Since the digits in "11" are the same, the output is true.

Example 2:

Input: s = "34789"

Output: false

Explanation:

Constraints:

Check If Digits Are Equal in String After Operations II - Solution & Explanation