Problem:- https://atcoder.jp/contests/abc122/tasks/abc122_d

I can't figure out what is wrong with my DP solution.

https://p.ip.fi/dn_u

The DP state dp[i][j][k] represents number of strings of length i with last letters j and k. The letters A,G,C and T are 0,1,2 and 3 respectively. It doesn't work from n=4.

Thank you.