Merge pull request #90 from remy727/2141-maximum-running-time-of-n-computers

2141. Maximum Running Time of N Computers

Author: remy727

README.md

@@ -342,6 +342,7 @@
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+| 2141 | Maximum Running Time of N Computers | [Ruby](./algorithms/ruby/2141-maximum-running-time-of-n-computers.rb) | Hard |
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algorithms/ruby/2141-maximum-running-time-of-n-computers.rb

@@ -0,0 +1,68 @@
+# frozen_string_literal: true
+
+# 2141. Maximum Running Time of N Computers
+# Hard
+# https://leetcode.com/problems/maximum-running-time-of-n-computers
+
+=begin
+You have n computers. You are given the integer n and a 0-indexed integer array batteries where the ith battery can run a computer for batteries[i] minutes. You are interested in running all n computers simultaneously using the given batteries.
+Initially, you can insert at most one battery into each computer. After that and at any integer time moment, you can remove a battery from a computer and insert another battery any number of times. The inserted battery can be a totally new battery or a battery from another computer. You may assume that the removing and inserting processes take no time.
+Note that the batteries cannot be recharged.
+Return the maximum number of minutes you can run all the n computers simultaneously.
+
+Example 1:
+Input: n = 2, batteries = [3,3,3]
+Output: 4
+Explanation:
+Initially, insert battery 0 into the first computer and battery 1 into the second computer.
+After two minutes, remove battery 1 from the second computer and insert battery 2 instead. Note that battery 1 can still run for one minute.
+At the end of the third minute, battery 0 is drained, and you need to remove it from the first computer and insert battery 1 instead.
+By the end of the fourth minute, battery 1 is also drained, and the first computer is no longer running.
+We can run the two computers simultaneously for at most 4 minutes, so we return 4.
+
+Example 2:
+Input: n = 2, batteries = [1,1,1,1]
+Output: 2
+Explanation:
+Initially, insert battery 0 into the first computer and battery 2 into the second computer.
+After one minute, battery 0 and battery 2 are drained so you need to remove them and insert battery 1 into the first computer and battery 3 into the second computer.
+After another minute, battery 1 and battery 3 are also drained so the first and second computers are no longer running.
+We can run the two computers simultaneously for at most 2 minutes, so we return 2.
+
+Constraints:
+* 1 <= n <= batteries.length <= 105
+* 1 <= batteries[i] <= 109
+=end
+
+# @param {Integer} n
+# @param {Integer[]} batteries
+# @return {Integer}
+def max_run_time(n, batteries)
+  batteries.sort!
+
+  extra = batteries[0...-n].sum
+
+  live = batteries[-n..]
+
+  for i in (0...n - 1)
+    if extra / (i + 1) < live[i + 1] - live[i]
+      return live[i] + extra / (i + 1)
+    end
+
+    extra -= (i + 1) * (live[i + 1] - live[i])
+  end
+
+  live[-1] + extra / n
+end
+
+# **************** #
+#       TEST       #
+# **************** #
+
+require "test/unit"
+class Test_max_run_time < Test::Unit::TestCase
+  def test_
+    assert_equal 4, max_run_time(2, [3, 3, 3])
+    assert_equal 2, max_run_time(2, [1, 1, 1, 1])
+  end
+end