Problem 680

[EliteToday]

Hi Everyone, I was working on the newest problem. But the following is unclear.

The question says that for some K iterations, one array value needs to be swapped with another array value in A. However the example does two swaps in one of the steps. Here indicated in red:

Initial position: (0,1,2,3,4)
Step 1 - Reverse A[1] to A[1]: (0,1,2,3,4)
Step 2 - Reverse A[2] to A[3]: (0,1,3,2,4)
Step 3 - Reverse A[0] to A[3]: (2,3,1,0,4)
Step 4 - Reverse A[3] to A[1]: (2,0,1,3,4)
R(5,4)=0×2+1×0+2×1+3×3+4×4=27

Without this additional swapping, the solution would be:
R(5,4)=0×2+1×0+2×3+3×1+4×4=25

In don't understand why this is happening, is there an error in the explanation or have i misinterpreted the question here. Hope someone knows!

Thanks in Advance

[DJohn]

The question says that for some K iterations, one array value needs to be swapped with another array value in A.

That is not what the question says.

the $j$-th operation consists of reversing the order of those elements in $A$ with indices between $s_j$ and $t_j$

So if the array is 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 and the step is to reverse the elements between 3 and 8, we take those elements (3, 4, 5, 6, 7, 8), reverse them (giving 8, 7, 6, 5, 4, 3), and put them back in the array. The final result is 0, 1, 2, 8, 7, 6, 5, 4, 3, 9, 10.

[EliteToday]

Thank you very much, this clarifies a lot.
I misinterpreted the meaning of "between" here.

Back to the drawing board...