Given an array of integers, determine whether the array can be sorted in ascending order using only one of the following operations one time.
- Swap two elements.
- Reverse one sub-segment.
Determine whether one, both or neither of the operations will complete the task. If both work, choose swap. For instance, given an array either swap the and , or reverse them to sort the array. Choose swap. The Output Format section below details requirements.
Complete the almostSorted function in the editor below. It should print the results and return nothing.
almostSorted has the following parameter(s):
- arr: an array of integers
The first line contains a single integer , the size of .
The next line contains space-separated integers where .
All are distinct.
- If the array is already sorted, output yes on the first line. You do not need to output anything else.
If you can sort this array using one single operation (from the two permitted operations) then output yes on the first line and then:
a. If elements can be swapped, and , output swap l r in the second line. and are the indices of the elements to be swapped, assuming that the array is indexed from to .
b. Otherwise, when reversing the segment , output reverse l r in the second line. and are the indices of the first and last elements of the subsequence to be reversed, assuming that the array is indexed from to .
represents the sub-sequence of the array, beginning at index and ending at index , both inclusive.
If an array can be sorted by either swapping or reversing, choose swap.
- If you cannot sort the array either way, output no on the first line.
Sample Input 1
2 4 2
Sample Output 1
yes swap 1 2
You can either swap(1, 2) or reverse(1, 2). You prefer swap.
Sample Input 2
3 3 1 2
Sample Output 2
It is impossible to sort by one single operation.
Sample Input 3
6 1 5 4 3 2 6
Sample Output 3
yes reverse 2 5
You can reverse the sub-array d[2...5] = "5 4 3 2", then the array becomes sorted.
Solution in Python
def almostSorted(a): x = 0 y = len(a)-1 while a[x]<=a[x+1]: x+=1 while a[y]>=a[y-1]: y-=1 b = a[x:y+1] b,b[-1]=b[-1],b cond_l = True if x-1<0 else b>=a[x-1] cond_r = True if y+1==len(a) else a[y+1]>=b[-1] if cond_l and cond_r: for i in range(len(b)-1): if b[i]>b[i+1]: break else: return "yes\nswap %s %s"%(x+1,y+1) b,b[-1]=b[-1],b cond_l = True if x-1<0 else a[x-1]<=b[-1] cond_r = True if y+1==len(a) else b<=a[y+1] if cond_l and cond_r: for i in range(len(b)-1): if b[i]<b[i+1]: break else: return "yes\nreverse %s %s"%(x+1,y+1) return "no" n = int(input()) arr = list(map(int, input().split())) print(almostSorted(arr))