675. Cut Off Trees for Golf Event

Hard

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635

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.- A number greater than
`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.

You 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.

**Example 1:**

Input:forest = [[1,2,3],[0,0,4],[7,6,5]]Output:6Explanation:Following the path above allows you to cut off the trees from shortest to tallest in 6 steps.

**Example 2:**

Input:forest = [[1,2,3],[0,0,0],[7,6,5]]Output:-1Explanation:The trees in the bottom row cannot be accessed as the middle row is blocked.

**Example 3:**

Input:forest = [[2,3,4],[0,0,5],[8,7,6]]Output:6Explanation:You can follow the same path as Example 1 to cut off all the trees. Note that you can cut off the first tree at (0, 0) before making any steps.

**Constraints:**

`m == forest.length`

`n == forest[i].length`

`1 <= m, n <= 50`

`0 <= forest[i][j] <= 10`

^{9}- Heights of all trees are
**distinct**.

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