1631-path-with-minimum-effort.rb

# frozen_string_literal: true

# 1631. Path With Minimum Effort
# Medium
# https://leetcode.com/problems/path-with-minimum-effort

=begin
You are a hiker preparing for an upcoming hike. You are given heights, a 2D array of size rows x columns, where heights[row][col] represents the height of cell (row, col). You are situated in the top-left cell, (0, 0), and you hope to travel to the bottom-right cell, (rows-1, columns-1) (i.e., 0-indexed). You can move up, down, left, or right, and you wish to find a route that requires the minimum effort.
A route's effort is the maximum absolute difference in heights between two consecutive cells of the route.
Return the minimum effort required to travel from the top-left cell to the bottom-right cell.

Example 1:
Input: heights = [[1,2,2],[3,8,2],[5,3,5]]
Output: 2
Explanation: The route of [1,3,5,3,5] has a maximum absolute difference of 2 in consecutive cells.
This is better than the route of [1,2,2,2,5], where the maximum absolute difference is 3.

Example 2:
Input: heights = [[1,2,3],[3,8,4],[5,3,5]]
Output: 1
Explanation: The route of [1,2,3,4,5] has a maximum absolute difference of 1 in consecutive cells, which is better than route [1,3,5,3,5].

Example 3:
Input: heights = [[1,2,1,1,1],[1,2,1,2,1],[1,2,1,2,1],[1,2,1,2,1],[1,1,1,2,1]]
Output: 0
Explanation: This route does not require any effort.

Constraints:
* rows == heights.length
* columns == heights[i].length
* 1 <= rows, columns <= 100
* 1 <= heights[i][j] <= 106
=end

# @param {Integer[][]} heights
# @return {Integer}
defminimum_effort_path(heights)
h=heights.size
w=heights[0].size
queue=[[0,0]]
cost=Array.new(h).map{Array.new(w,Float::INFINITY)}
cost[0][0]=0
directions=[[1,0],[0,1],[-1,0],[0, -1]]
inside=->(rr,cc){rr.between?(0,h - 1) && cc.between?(0,w - 1)}
while ! queue.empty?
r,c=queue.pop()
curr_h=heights[r][c]
curr_c=cost[r][c]
directions.eachdo |(dr,dc)|
r1,c1=r + dr,c + dc
ifinside[r1,c1]
nh=heights[r1][c1]
nc=(curr_h - nh).abs > curr_c ? (curr_h - nh).abs : curr_c
ifnc < cost[r1][c1]
cost[r1][c1]=nc
queue.unshift[r1,c1]
end
end
end
end
cost[h - 1][w - 1]
end

# **************** #
# TEST #
# **************** #

require"test/unit"
classTest_minimum_effort_path < Test::Unit::TestCase
deftest_
assert_equal2,minimum_effort_path([[1,2,2],[3,8,2],[5,3,5]])
assert_equal1,minimum_effort_path([[1,2,3],[3,8,4],[5,3,5]])
assert_equal0,minimum_effort_path([[1,2,1,1,1],[1,2,1,2,1],[1,2,1,2,1],[1,2,1,2,1],[1,1,1,2,1]])
end
end