1536 - Minimum Swaps to Arrange a Binary Grid.

Medium

Given an n x n binary grid, in one step you can choose two adjacent rows of the grid and swap them.

A grid is said to be valid if all the cells above the main diagonal are zeros.

Return the minimum number of steps needed to make the grid valid, or \-1 if the grid cannot be valid.

The main diagonal of a grid is the diagonal that starts at cell (1, 1) and ends at cell (n, n).

Example 1:

Input: grid = \[\[0,0,1],1,1,0,1,0,0]

Output: 3

Example 2:

Input: grid = \[\[0,1,1,0],0,1,1,0,0,1,1,0,0,1,1,0]

Output: -1

Explanation: All rows are similar, swaps have no effect on the grid.

Example 3:

Input: grid = \[\[1,0,0],1,1,0,1,1,1]

Output: 0

Constraints:

• n == grid.length == grid[i].length

• 1 <= n <= 200

• grid[i][j] is either 0 or 1