Cells in a Range on an Excel Sheet

A cell (r, c) of an Excel sheet is represented as a string "<col><row>" where:

• <col> denotes the column number c of the cell. It is represented by alphabetical letters. For example, the 1^st column is denoted by 'A', the 2^nd by 'B', the 3^rd by 'C', and so on.
• <row> is the row number r of the cell. The r^th row is represented by the integer r.

You are given a string s in the format "<col1><row1>:<col2><row2>", where <col1> represents the column c1, <row1> represents the row r1, <col2> represents the column c2, and <row2> represents the row r2, such that r1 <= r2 and c1 <= c2.

Return the list of cells (x, y) such that r1 <= x <= r2 and c1 <= y <= c2. The cells should be represented as strings in the format mentioned above and be sorted in non-decreasing order first by columns and then by rows.