Find the Original Typed String II
Alice is attempting to type a specific string on her computer. However, she tends to be clumsy and may press a key for too long, resulting in a character being typed multiple times.
You are given a string word, which represents the final output displayed on Alice's screen. You are also given a positive integer k.
Return the total number of possible original strings that Alice might have intended to type, if she was trying to type a string of size at least k.
Since the answer may be very large, return it modulo 10^9 + 7.
Example 1
Input
word = "aabbccdd", k = 7Output
5The possible strings are: "aabbccdd", "aabbccd", "aabbcdd", "aabccdd", and "abbccdd".
Example 2
Input
word = "aabbccdd", k = 8Output
1The only possible string is "aabbccdd".
Constraints
- 1 <= word.length <= 5 * 10^5
- word consists only of lowercase English letters.
- 1 <= k <= 2000