{ "data": { "question": { "questionId": "675", "questionFrontendId": "675", "categoryTitle": "Algorithms", "boundTopicId": 1226, "title": "Cut Off Trees for Golf Event", "titleSlug": "cut-off-trees-for-golf-event", "content": "
You are asked to cut off all the trees in a forest for a golf event. The forest is represented as an m x n
matrix. In this matrix:
0
means the cell cannot be walked through.1
represents an empty cell that can be walked through.1
represents a tree in a cell that can be walked through, and this number is the tree's height.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.
\n\nYou must cut off the trees in order from shortest to tallest. When you cut off a tree, the value at its cell becomes 1
(an empty cell).
Starting from the point (0, 0)
, return the minimum steps you need to walk to cut off all the trees. If you cannot cut off all the trees, return -1
.
Note: 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.
\n\n\n
Example 1:
\n\n\nInput: forest = [[1,2,3],[0,0,4],[7,6,5]]\nOutput: 6\nExplanation: Following the path above allows you to cut off the trees from shortest to tallest in 6 steps.\n\n\n
Example 2:
\n\n\nInput: forest = [[1,2,3],[0,0,0],[7,6,5]]\nOutput: -1\nExplanation: The trees in the bottom row cannot be accessed as the middle row is blocked.\n\n\n
Example 3:
\n\n\nInput: forest = [[2,3,4],[0,0,5],[8,7,6]]\nOutput: 6\nExplanation: You can follow the same path as Example 1 to cut off all the trees.\nNote that you can cut off the first tree at (0, 0) before making any steps.\n\n\n
\n
Constraints:
\n\nm == forest.length
n == forest[i].length
1 <= m, n <= 50
0 <= forest[i][j] <= 109
你被请来给一个要举办高尔夫比赛的树林砍树。树林由一个 m x n
的矩阵表示, 在这个矩阵中:
0
表示障碍,无法触碰1
表示地面,可以行走比 1 大的数
表示有树的单元格,可以行走,数值表示树的高度每一步,你都可以向上、下、左、右四个方向之一移动一个单位,如果你站的地方有一棵树,那么你可以决定是否要砍倒它。
\n\n你需要按照树的高度从低向高砍掉所有的树,每砍过一颗树,该单元格的值变为 1
(即变为地面)。
你将从 (0, 0)
点开始工作,返回你砍完所有树需要走的最小步数。 如果你无法砍完所有的树,返回 -1
。
可以保证的是,没有两棵树的高度是相同的,并且你至少需要砍倒一棵树。
\n\n\n\n
示例 1:
\n\n\n输入:forest = [[1,2,3],[0,0,4],[7,6,5]]\n输出:6\n解释:沿着上面的路径,你可以用 6 步,按从最矮到最高的顺序砍掉这些树。\n\n
示例 2:
\n\n\n输入:forest = [[1,2,3],[0,0,0],[7,6,5]]\n输出:-1\n解释:由于中间一行被障碍阻塞,无法访问最下面一行中的树。\n\n\n
示例 3:
\n\n\n输入:forest = [[2,3,4],[0,0,5],[8,7,6]]\n输出:6\n解释:可以按与示例 1 相同的路径来砍掉所有的树。\n(0,0) 位置的树,可以直接砍去,不用算步数。\n\n\n
\n\n
提示:
\n\nm == forest.length
n == forest[i].length
1 <= m, n <= 50
0 <= forest[i][j] <= 109
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