(a[i]-1)/y represents row in which a[i] lies.[e.g. let y=4 and a[i]=5, then (5-1)/4=1 means 5 belongs to row 1(0 indexed)]. (a[i]-1)/y != (a[i-1]-1)/y this condition can be used if a[i] and a[i-1] differ by 1. It basically checks whether a[i] and a[i-1] differing by 1 belong same row or not.

You need to find the differences b/w the values of two consecutive cells. There should be only two difference values : 1. '1' for any two consecutive elements in a row. 2. 'y'(no of columns) for any two consecutive elements in a column(one above other).

There is no constraint on number of rows(x). So you can output 1e9 for each case. Note : Also you need to check the border contraints.