Package g0901_1000.s0980_unique_paths_iii

Class Solution

java.lang.Object
g0901_1000.s0980_unique_paths_iii.Solution
public class Solution extends java.lang.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 Summary

    Constructors
    Constructor
    Description
    Solution()
     

  • Method Summary

    Modifier and Type
    Method
    Description
    int
    uniquePathsIII(int[][] grid)
     

    Methods inherited from class java.lang.Object

    clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

  • Constructor Details

    • Solution

      public Solution()

  • Method Details

    • uniquePathsIII

      public int uniquePathsIII(int[][] grid)