Reverse One Segment
Can the list be made non-decreasing by reversing exactly one contiguous segment (possibly of length 1)?
Input: the first line has N; the second line has N integers.
Output: YES or NO.
Constraints:
- 1 ≤ N ≤ 105
- −109 ≤ ai ≤ 109
Sample Tests
Input 1
5 1 5 4 3 6
Output 1
YES
Input 2
4 2 1 4 3
Output 2
NO
Discussion (opens after you solve — no spoilers before)
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