Shortest Path in an Obstructed Grid

You are given a grid of size $n \times m$, where each cell is either open (represented by 0) or blocked (represented by 1). Your task is to find the length of the shortest path from the top-left cell $(0,0)$ to the bottom-right cell $(n-1, m-1)$.

The movement is restricted to horizontal and vertical directions only (up, down, left, and right). If no valid path exists, output -1.

Note: The grid indices satisfy $0 \le i < n$ and $0 \le j < m$, and the starting cell as well as the ending cell must be open (i.e. have a value of 0).

inputFormat

The first line contains two space-separated integers n and m, representing the number of rows and columns, respectively. The next n lines each contain m space-separated integers (each integer is either 0 or 1), representing the grid.

outputFormat

Output a single integer: the length of the shortest path from the top-left corner to the bottom-right corner. If no such path exists, output -1.

2 2
0 1
1 0

-1