There is an 8 x 8 empty chessboard with 1-indexed rows and columns.
You are given an array source = [sr, sc] representing the starting position of a bishop, and an array target = [tr, tc] representing the target position.
In one move, the bishop travels one or more squares along a single diagonal direction, staying within the board.
Return the minimum number of moves for the bishop to land exactly on target. If it can never reach target, return -1.
Example 1:
Input: source = [8,1], target = [1,8]
Output: 1
Explanation:
A single diagonal move takes the bishop straight from (8, 1) to (1, 8).
Example 2:
Input: source = [4,2], target = [1,3]
Output: 2
Explanation:
The bishop moves from (4, 2) to (3, 1), then from (3, 1) to (1, 3), reaching the target in 2 moves.
Example 3:
Input: source = [1,1], target = [3,4]
Output: -1
Explanation:
No matter how many diagonal moves it makes, the bishop starting at (1, 1) can never land on (3, 4). Thus, the answer is -1.
Constraints:
source.length == target.length == 21 <= sr, sc, tr, tc <= 8source != target