Shortest Path in a Grid

You are given a grid consisting of m rows and n columns. Each cell of the grid contains either 0 or 1. A value of 0 indicates that the cell is free to move into, and 1 indicates an obstacle.

Your task is to compute the shortest path from the top-left corner (cell (0,0)) to the bottom-right corner (cell (m-1, n-1)). The path length is defined as the number of cells in the path including both the starting and ending cells. You may move only in four directions: up, down, left, and right. If there is no valid path, return -1.

Note: The answer should be produced using a breadth-first search (BFS) strategy to account for grid obstacles. When counting steps, the starting cell is counted as 1.

The problem can be formulated using the following LaTeX equations:

Grid size: \(m \times n\).
Path length from \((0,0)\) to \((m-1,n-1)\): \(d\) such that the path is the shortest.
If no path exists, output \(-1\).

inputFormat

The input is read from stdin and is formatted as follows:

1. The first line contains two integers, m and n, separated by a space, representing the number of rows and columns respectively.
2. The next m lines contain n integers each. Each integer is either 0 or 1, representing the grid cells.

outputFormat

Output the length of the shortest path from the top-left to the bottom-right cell. If there is no valid path, output -1. The result is printed to stdout.

## sample

3 3
0 1 0
0 1 0
0 0 0

5

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