Package g0901_1000.s0980_unique_paths_iii

Class Solution

  • public class Solution
extends Object
    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.

    • Constructor Detail

      • Solution

        public Solution()

    • Method Detail

      • uniquePathsIII

        public int uniquePathsIII​(int[][] grid)