I was solving problem 279C (Ladders)
My logic is to create two arrays inc and dec
inc[i] contains the largest j, such that i<=j and the sequence from a_i, a_i+1, ..., a_j is increasing.
dec[i] contains minimum j, such that i>=j and the sequence from a_j, a_j+1, ..., a_i is decreasing.
Now the sequence l,r is ladder if inc[l-1]==dec[r-1] || inc[l-1]>=r-1 || dec[r-1]<=l-1 (I used 0 based indexing)
I am getting WA on test 20, please help me!
Solution Link
Thanks in advance!