LeetCode in Kotlin

980. Unique Paths III

Hard

You are given an m x n integer array grid where grid[i][j] could be:

• 1 representing the starting square. There is exactly one starting square.
• 2 representing the ending square. There is exactly one ending square.
• 0 representing empty squares we can walk over.
• -1 representing obstacles that we cannot walk over.

Return the number of 4-directional walks from the starting square to the ending square, that walk over every non-obstacle square exactly once.

Example 1:

Input: grid = [[1,0,0,0],[0,0,0,0],[0,0,2,-1]]

Output: 2

Explanation: We have the following two paths:

1. (0,0),(0,1),(0,2),(0,3),(1,3),(1,2),(1,1),(1,0),(2,0),(2,1),(2,2)
2. (0,0),(1,0),(2,0),(2,1),(1,1),(0,1),(0,2),(0,3),(1,3),(1,2),(2,2)

Example 2:

Input: grid = [[1,0,0,0],[0,0,0,0],[0,0,0,2]]

Output: 4

Explanation: We have the following four paths:

1. (0,0),(0,1),(0,2),(0,3),(1,3),(1,2),(1,1),(1,0),(2,0),(2,1),(2,2),(2,3)
2. (0,0),(0,1),(1,1),(1,0),(2,0),(2,1),(2,2),(1,2),(0,2),(0,3),(1,3),(2,3)
3. (0,0),(1,0),(2,0),(2,1),(2,2),(1,2),(1,1),(0,1),(0,2),(0,3),(1,3),(2,3)
4. (0,0),(1,0),(2,0),(2,1),(1,1),(0,1),(0,2),(0,3),(1,3),(1,2),(2,2),(2,3)

Example 3:

Input: grid = [[0,1],[2,0]]

Output: 0

Explanation: There is no path that walks over every empty square exactly once. Note that the starting and ending square can be anywhere in the grid.

Constraints:

• m == grid.length
• n == grid[i].length
• 1 <= m, n <= 20
• 1 <= m * n <= 20
• -1 <= grid[i][j] <= 2
• There is exactly one starting cell and one ending cell.

Solution

class Solution {
    private val row = intArrayOf(0, 0, 1, -1)
    private val col = intArrayOf(1, -1, 0, 0)

    private fun isSafe(grid: Array<IntArray>, rows: Int, cols: Int, i: Int, j: Int): Int {
        if (i < 0 || j < 0 || i >= rows || j >= cols || grid[i][j] == -1) {
            return 0
        }
        if (grid[i][j] == 2) {
            for (l in 0 until rows) {
                for (m in 0 until cols) {
                    if (grid[l][m] == 0) {
                        /* Return 0 if all zeros in the path are not covered */
                        return 0
                    }
                }
            }
            /* Return 1, as we covered all zeros in the path */
            return 1
        }
        /* mark as visited */
        grid[i][j] = -1
        var result = 0
        for (k in 0..3) {
            /* travel in all four directions (up,down,right,left) */
            result += isSafe(grid, rows, cols, i + row[k], j + col[k])
        }
        /* Mark unvisited again to backtrack */
        grid[i][j] = 0
        return result
    }

    fun uniquePathsIII(grid: Array<IntArray>): Int {
        val rows = grid.size
        val cols = grid[0].size
        var result = 0
        for (k in 0 until rows) {
            for (m in 0 until cols) {
                if (grid[k][m] == 1) {
                    /* find indexes where 1 is located and start covering paths */
                    result = isSafe(grid, rows, cols, k, m)
                    break
                }
            }
        }
        return result
    }
}

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