Do you mean you give the answer "0" for every L > 26 or S > 351 ( 1+2+3+4...+26)?
Do you mean the string "aaaaabbbbbbcccccc" is not strictly ascending?

repeating mamun question: can anyone please explain me how to apply dynamic programming in this problem, i just cant find the relation and got too many TLE already

Jemerson wrote:repeating mamun question: can anyone please explain me how to apply dynamic programming in this problem, i just cant find the relation and got too many TLE already

Denote f(l,s,c) the number of strictly increasing strings of length l ending with c, which sum is s. You can easily prove that:

f(l+1, s+c, c) = ∑'a' ≤ d < cf(l, s, d), where 0 ≤ l, 0 ≤ s and 'a' ≤ c ≤ 'z'.

After stating the trivial cases of the recurence, it may help you to find a DP solution.

Case 1: 2
Case 2: 0
Case 3: 4
Case 4: 0
Case 5: 0
Case 6: 1
Case 7: 4
Case 8: 0
Case 9: 0
Case 10: 0
Case 11: 1
Case 12: 0
Case 13: 6
Case 14: 52
Case 15: 1
Case 16: 10
Case 17: 46
Case 18: 4
Case 19: 10
Case 20: 2
Case 21: 67
Case 22: 0
Case 23: 9
Case 24: 46
Case 25: 66
Case 26: 0
Case 27: 0
Case 28: 80
Case 29: 72
Case 30: 1
Case 31: 12
Case 32: 36
Case 33: 35
Case 35: 14

Case 1: 3
Case 2: 0
Case 3: 4
Case 4: 0
Case 5: 0
Case 6: 1
Case 7: 4
Case 8: 0
Case 9: 0
Case 10: 0
Case 11: 1
Case 12: 4605
Case 13: 15
Case 14: 73
Case 15: 1
Case 16: 18
Case 17: 3729
Case 18: 5
Case 19: 22
Case 20: 2
Case 21: 149
Case 22: 280
Case 23: 9
Case 24: 76
Case 25: 398
Case 26: 0
Case 27: 0
Case 28: 1972
Case 29: 2611
Case 30: 1
Case 31: 12
Case 32: 44
Case 33: 64
Case 34: 37

4th and 5th test cases in your input are invalid -- L and S must be both greater than zero.