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53 lines
2.5 KiB
HTML
53 lines
2.5 KiB
HTML
<p>You are asked to cut off all the trees in a forest for a golf event. The forest is represented as an <code>m x n</code> matrix. In this matrix:</p>
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<ul>
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<li><code>0</code> means the cell cannot be walked through.</li>
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<li><code>1</code> represents an empty cell that can be walked through.</li>
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<li>A number greater than <code>1</code> represents a tree in a cell that can be walked through, and this number is the tree's height.</li>
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</ul>
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<p>In one step, you can walk in any of the four directions: north, east, south, and west. If you are standing in a cell with a tree, you can choose whether to cut it off.</p>
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<p>You must cut off the trees in order from shortest to tallest. When you cut off a tree, the value at its cell becomes <code>1</code> (an empty cell).</p>
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<p>Starting from the point <code>(0, 0)</code>, return <em>the minimum steps you need to walk to cut off all the trees</em>. If you cannot cut off all the trees, return <code>-1</code>.</p>
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<p><strong>Note:</strong> The input is generated such that no two trees have the same height, and there is at least one tree needs to be cut off.</p>
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<p> </p>
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<p><strong class="example">Example 1:</strong></p>
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<img alt="" src="https://assets.leetcode.com/uploads/2020/11/26/trees1.jpg" style="width: 242px; height: 242px;" />
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<pre>
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<strong>Input:</strong> forest = [[1,2,3],[0,0,4],[7,6,5]]
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<strong>Output:</strong> 6
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<strong>Explanation:</strong> Following the path above allows you to cut off the trees from shortest to tallest in 6 steps.
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</pre>
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<p><strong class="example">Example 2:</strong></p>
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<img alt="" src="https://assets.leetcode.com/uploads/2020/11/26/trees2.jpg" style="width: 242px; height: 242px;" />
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<pre>
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<strong>Input:</strong> forest = [[1,2,3],[0,0,0],[7,6,5]]
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<strong>Output:</strong> -1
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<strong>Explanation:</strong> The trees in the bottom row cannot be accessed as the middle row is blocked.
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</pre>
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<p><strong class="example">Example 3:</strong></p>
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<pre>
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<strong>Input:</strong> forest = [[2,3,4],[0,0,5],[8,7,6]]
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<strong>Output:</strong> 6
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<b>Explanation:</b> You can follow the same path as Example 1 to cut off all the trees.
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Note that you can cut off the first tree at (0, 0) before making any steps.
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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 == forest.length</code></li>
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<li><code>n == forest[i].length</code></li>
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<li><code>1 <= m, n <= 50</code></li>
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<li><code>0 <= forest[i][j] <= 10<sup>9</sup></code></li>
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<li>Heights of all trees are <strong>distinct</strong>.</li>
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</ul>
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