# ---
# title: 675. Cut Off Trees for Golf Event
# id: problem675
# author: Tian Jun
# date: 2020-10-31
# difficulty: Hard
# categories: Breadth-first Search
# link: <https://leetcode.com/problems/cut-off-trees-for-golf-event/description/>
# hidden: true
# ---
# 
# 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`.
# 
# You are guaranteed that no two trees have the same height, and there is at
# least one tree needs to be cut off.
# 
# 
# 
# **Example 1:**
# 
# ![](https://assets.leetcode.com/uploads/2020/11/26/trees1.jpg)
# 
#     
#     
#     Input: forest = [[1,2,3],[0,0,4],[7,6,5]]
#     Output: 6
#     Explanation: Following the path above allows you to cut off the trees from shortest to tallest in 6 steps.
#     
# 
# **Example 2:**
# 
# ![](https://assets.leetcode.com/uploads/2020/11/26/trees2.jpg)
# 
#     
#     
#     Input: forest = [[1,2,3],[0,0,0],[7,6,5]]
#     Output: -1
#     Explanation: 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: 6
#     Explanation: 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] <= 109`
# 
# 
## @lc code=start
using LeetCode

## add your code here:
## @lc code=end
