3744. Find Kth Character in Expanded String

You are given a string s consisting of one or more words separated by single spaces. Each word in s consists of lowercase English letters.

We obtain the expanded string t from s as follows:

• For each word in s, repeat its first character once, then its second character twice, and so on.

For example, if s = "hello world", then t = "heelllllllooooo woorrrllllddddd".

You are also given an integer k, representing a valid index of the string t.

Return the kth character of the string t.

class Solution {
public:
    char kthCharacter(string s, long long k) {
        int len = 0;
        k++;
        for(auto& ch : s) {
            if(isalpha(ch)) len++;
            else len = 0;
            k -= max(len, 1);
            if(k <= 0) return ch;
        }
        return '#';
    }
};