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Grokking the Coding Interview Patterns in C#

Solution: Minimum Cost to Make at Least One Valid Path in a Grid

Explore how to determine the minimum cost to create at least one valid path from the top-left to bottom-right of a grid by modifying directional signs. Learn to implement a 0-1 BFS algorithm with a deque to efficiently prioritize lower-cost path expansions and understand the time and space complexity involved in this graph problem.

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Statement

You are given an m×nm \times n grid, where each cell contains a directional sign indicating which neighboring cell to move to next. The sign in a cell grid[i][j] can be:

  • 1: Move right, i.e., from grid[i][j] to grid[i][j + 1].

  • 2: Move left, i.e., from grid[i][j] to grid[i][j - 1].

  • 3: Move down, i.e., from grid[i][j] to grid[i + 1][j].

  • 4: Move up, i.e., from grid[i][j] to grid[i - 1][j].

Note: Some signs may point outside the boundaries of the grid.

Your starting position is the top-left cell (0,0)(0, 0). A valid path is any sequence of moves beginning at (0,0)(0,0) and ending at the bottom-right cell (m−1 ...