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55 lines
2.4 KiB
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55 lines
2.4 KiB
HTML
<p>You are given an <code>m x n</code> integer array <code>grid</code> where <code>grid[i][j]</code> could be:</p>
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<ul>
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<li><code>1</code> representing the starting square. There is exactly one starting square.</li>
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<li><code>2</code> representing the ending square. There is exactly one ending square.</li>
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<li><code>0</code> representing empty squares we can walk over.</li>
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<li><code>-1</code> representing obstacles that we cannot walk over.</li>
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</ul>
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<p>Return <em>the number of 4-directional walks from the starting square to the ending square, that walk over every non-obstacle square exactly once</em>.</p>
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<p> </p>
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<p><strong>Example 1:</strong></p>
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<img alt="" src="https://assets.leetcode.com/uploads/2021/08/02/lc-unique1.jpg" style="width: 324px; height: 245px;" />
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<pre>
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<strong>Input:</strong> grid = [[1,0,0,0],[0,0,0,0],[0,0,2,-1]]
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<strong>Output:</strong> 2
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<strong>Explanation:</strong> We have the following two paths:
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1. (0,0),(0,1),(0,2),(0,3),(1,3),(1,2),(1,1),(1,0),(2,0),(2,1),(2,2)
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2. (0,0),(1,0),(2,0),(2,1),(1,1),(0,1),(0,2),(0,3),(1,3),(1,2),(2,2)
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</pre>
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<p><strong>Example 2:</strong></p>
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<img alt="" src="https://assets.leetcode.com/uploads/2021/08/02/lc-unique2.jpg" style="width: 324px; height: 245px;" />
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<pre>
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<strong>Input:</strong> grid = [[1,0,0,0],[0,0,0,0],[0,0,0,2]]
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<strong>Output:</strong> 4
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<strong>Explanation:</strong> We have the following four paths:
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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)
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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)
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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)
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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)
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</pre>
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<p><strong>Example 3:</strong></p>
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<img alt="" src="https://assets.leetcode.com/uploads/2021/08/02/lc-unique3-.jpg" style="width: 164px; height: 165px;" />
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<pre>
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<strong>Input:</strong> grid = [[0,1],[2,0]]
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<strong>Output:</strong> 0
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<strong>Explanation:</strong> There is no path that walks over every empty square exactly once.
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Note that the starting and ending square can be anywhere in the grid.
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</pre>
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<p> </p>
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<p><strong>Constraints:</strong></p>
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<ul>
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<li><code>m == grid.length</code></li>
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<li><code>n == grid[i].length</code></li>
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<li><code>1 <= m, n <= 20</code></li>
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<li><code>1 <= m * n <= 20</code></li>
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<li><code>-1 <= grid[i][j] <= 2</code></li>
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<li>There is exactly one starting cell and one ending cell.</li>
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</ul>
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