| You want to write an image detection system that is able to recognize | |
| different geometric shapes. In the first version of the system you settled | |
| with just being able to detect filled squares on a grid. | |
| You are given a grid of **N**×**N** square cells. Each cell is either white or | |
| black. Your task is to detect whether all the black cells form a square shape. | |
| ### Input | |
| The first line of the input consists of a single number **T**, the number of | |
| test cases. | |
| Each test case starts with a line containing a single integer **N**. Each of | |
| the subsequent **N** lines contain **N** characters. Each character is either | |
| "." symbolizing a white cell, or "#" symbolizing a black cell. Every test case | |
| contains at least one black cell. | |
| ### Output | |
| For each test case **i** numbered from 1 to **T**, output "Case #**i**: ", | |
| followed by YES or NO depending on whether or not all the black cells form a | |
| completely filled square with edges parallel to the grid of cells. | |
| ### Constraints | |
| 1 ≤ **T** ≤ 20 | |
| 1 ≤ **N** ≤ 20 | |
| ### Example | |
| Test cases 1 and 5 represent valid squares. Case 2 has an extra cell that is | |
| outside of the square. Case 3 shows a square not filled inside. And case 4 is | |
| a rectangle but not a square. | |