Score : 200 points
We have a sequence p = {p_1,\ p_2,\ ...,\ p_N} which is a permutation of {1,\ 2,\ ...,\ N}.
You can perform the following operation at most once: choose integers i and j (1 \leq i < j \leq N), and swap p_i and p_j. Note that you can also choose not to perform it.
Print YES
if you can sort p in ascending order in this way, and NO
otherwise.
Input is given from Standard Input in the following format:
N p_1 p_2 ... p_N
Print YES
if you can sort p in ascending order in the way stated in the problem statement, and NO
otherwise.
5 5 2 3 4 1
YES
You can sort p in ascending order by swapping p_1 and p_5.
5 2 4 3 5 1
NO
In this case, swapping any two elements does not sort p in ascending order.
7 1 2 3 4 5 6 7
YES
p is already sorted in ascending order, so no operation is needed.