Need to FInd number of substring contain at least k repititve characters.
string length can be 5 X 10^4
k also can be 5 X 10-^4

Example:
Input:
"acaab" k = 3
Output : 2 ["acaa", "acaab"]
Input:
"accad" k = 2
Output: 6 ["acc","acca","accad","cc","cca","ccad"]

Can any one help me with the solution?