Leetcode Problem 980. Unique Paths III

980. Unique Paths III

Leetcode Solutions

Find the coordinates of the starting square and count the total number of non-obstacle squares.
Define a recursive function backtrack that takes the current position and the count of remaining squares to visit.
If the current square is the ending square and all non-obstacle squares have been visited, increment the path count.
Mark the current square as visited by setting it to -2 (in-place modification).
Explore the next squares in all four directions (up, down, left, right).
For each direction, check if the next square is within the grid, not an obstacle, and not visited.
Recursively call backtrack for the valid next square with the updated remaining squares count.
After exploring all directions, backtrack by marking the current square as unvisited (restoring its original value).
Return the path count after exploring all paths.

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