shortest path:2nodes]binary matrix #BFT

Q: given 2 cells in a binary matrix (1=black, 0=white=blocked), check the pair are connected and if yes return the shortest path. There exists a path of length 1 between any 2 cells IFF both are side by side or stack atop.

count paths between 2 bTree nodes #PimcoQ9 Ashish is arguably harder than this problem, but this problem allows moving in four directions.

binary-matrix island count #DeepakM technique is more applicable. A BFT path should work.

  • every reachable node is painted Green (like 2)
  • we give up after our queue is empty

https://github.com/tiger40490/repo1/blob/py1/py/grid/classic_connectedPair.py is the implementation, briefly tested.

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