From a3e281971647b7b8aa8a313e64ce78e1c8778b4f Mon Sep 17 00:00:00 2001
From: khoaxuantu <68913255+khoaxuantu@users.noreply.github.com>
Date: Tue, 7 May 2024 22:02:27 +0700
Subject: [PATCH] feat: add ruby codes - chapter greedy

---
 .../ruby/chapter_greedy/coin_change_greedy.rb | 50 ++++++++++++++++++
 .../chapter_greedy/fractional_knapsack.rb     | 51 +++++++++++++++++++
 codes/ruby/chapter_greedy/max_capacity.rb     | 37 ++++++++++++++
 .../chapter_greedy/max_product_cutting.rb     | 28 ++++++++++
 4 files changed, 166 insertions(+)
 create mode 100644 codes/ruby/chapter_greedy/coin_change_greedy.rb
 create mode 100644 codes/ruby/chapter_greedy/fractional_knapsack.rb
 create mode 100644 codes/ruby/chapter_greedy/max_capacity.rb
 create mode 100644 codes/ruby/chapter_greedy/max_product_cutting.rb

diff --git a/codes/ruby/chapter_greedy/coin_change_greedy.rb b/codes/ruby/chapter_greedy/coin_change_greedy.rb
new file mode 100644
index 0000000000..7882b44b11
--- /dev/null
+++ b/codes/ruby/chapter_greedy/coin_change_greedy.rb
@@ -0,0 +1,50 @@
+=begin
+File: coin_change_greedy.rb
+Created Time: 2024-05-07
+Author: Xuan Khoa Tu Nguyen (ngxktuzkai2000@gmail.com)
+=end
+
+### 零钱兑换：贪心 ###
+def coin_change_greedy(coins, amt)
+  # 假设 coins 列表有序
+  i = coins.length - 1
+  count = 0
+  # 循环进行贪心选择，直到无剩余金额
+  while amt > 0
+    # 找到小于且最接近剩余金额的硬币
+    while i > 0 && coins[i] > amt
+      i -= 1
+    end
+    # 选择 coins[i]
+    amt -= coins[i]
+    count += 1
+  end
+  # 若未找到可行方案， 则返回 -1
+  amt == 0 ? count : -1
+end
+
+### Driver Code ###
+if __FILE__ == $0
+  # 贪心：能够保证找到全局最优解
+  coins = [1, 5, 10, 20, 50, 100]
+  amt = 186
+  res = coin_change_greedy(coins, amt)
+  puts "\ncoins = #{coins}, amt = #{amt}"
+  puts "凑到 #{amt} 所需的最少硬币数量为 #{res}"
+
+  # 贪心：无法保证找到全局最优解
+  coins = [1, 20, 50]
+  amt = 60
+  res = coin_change_greedy(coins, amt)
+  puts "\ncoins = #{coins}, amt = #{amt}"
+  puts "凑到 #{amt} 所需的最少硬币数量为 #{res}"
+  puts "实际上需要的最少数量为 3 , 即 20 + 20 + 20"
+
+  # 贪心：无法保证找到全局最优解
+  coins = [1, 49, 50]
+  amt = 98
+  res = coin_change_greedy(coins, amt)
+  puts "\ncoins = #{coins}, amt = #{amt}"
+  puts "凑到 #{amt} 所需的最少硬币数量为 #{res}"
+  puts "实际上需要的最少数量为 2 , 即 49 + 49"
+end
diff --git a/codes/ruby/chapter_greedy/fractional_knapsack.rb b/codes/ruby/chapter_greedy/fractional_knapsack.rb
new file mode 100644
index 0000000000..5790f278da
--- /dev/null
+++ b/codes/ruby/chapter_greedy/fractional_knapsack.rb
@@ -0,0 +1,51 @@
+=begin
+File: fractional_knapsack.rb
+Created Time: 2024-05-07
+Author: Xuan Khoa Tu Nguyen (ngxktuzkai2000@gmail.com)
+=end
+
+### 物品 ###
+class Item
+  attr_accessor :w # 物品重量
+  attr_accessor :v # 物品价值
+
+  def initialize(w, v)
+    @w = w
+    @v = v
+  end
+end
+
+### 分数背包：贪心 ###
+def fractional_knapsack(wgt, val, cap)
+  # 创建物品列表，包含两个属性：重量，价值
+  items = wgt.each_with_index.map { |w, i| Item.new(w, val[i]) }
+  # 按照单位价值 item.v / item.w 从高到低进行排序
+  items.sort! { |a, b| (b.v.to_f / b.w) <=> (a.v.to_f / a.w) }
+  # 循环贪心选择
+  res = 0
+  for item in items
+    if item.w <= cap
+      # 若剩余容量充足，则将当前物品整个装进背包
+      res += item.v
+      cap -= item.w
+    else
+      # 若剩余容量不足，则将当前物品的一部分装进背包
+      res += (item.v.to_f / item.w) * cap
+      # 已无剩余容量，因此跳出循环
+      break
+    end
+  end
+  res
+end
+
+### Driver Code ###
+if __FILE__ == $0
+  wgt = [10, 20, 30, 40, 50]
+  val = [50, 120, 150, 210, 240]
+  cap = 50
+  n = wgt.length
+
+  # 贪心算法
+  res = fractional_knapsack(wgt, val, cap)
+  puts "不超过背包容量的最大物品价值为 #{res}"
+end
diff --git a/codes/ruby/chapter_greedy/max_capacity.rb b/codes/ruby/chapter_greedy/max_capacity.rb
new file mode 100644
index 0000000000..f08a09c9e4
--- /dev/null
+++ b/codes/ruby/chapter_greedy/max_capacity.rb
@@ -0,0 +1,37 @@
+=begin
+File: max_capacity.rb
+Created Time: 2024-05-07
+Author: Xuan Khoa Tu Nguyen (ngxktuzkai2000@gmail.com)
+=end
+
+### 最大容量：贪心 ###
+def max_capacity(ht)
+  # 初始化 i, j，使其分列数组两端
+  i, j = 0, ht.length - 1
+  # 初始最大容量为 0
+  res = 0
+
+  # 循环贪心选择，直至两板相遇
+  while i < j
+    # 更新最大容量
+    cap = [ht[i], ht[j]].min * (j - i)
+    res = [res, cap].max
+    # 向内移动短板
+    if ht[i] < ht[j]
+      i += 1
+    else
+      j -= 1
+    end
+  end
+
+  res
+end
+
+### Driver Code ###
+if __FILE__ == $0
+  ht = [3, 8, 5, 2, 7, 7, 3, 4]
+
+  # 贪心算法
+  res = max_capacity(ht)
+  puts "最大容量为 #{res}"
+end
diff --git a/codes/ruby/chapter_greedy/max_product_cutting.rb b/codes/ruby/chapter_greedy/max_product_cutting.rb
new file mode 100644
index 0000000000..cee7523719
--- /dev/null
+++ b/codes/ruby/chapter_greedy/max_product_cutting.rb
@@ -0,0 +1,28 @@
+=begin
+File: max_product_cutting.rb
+Created Time: 2024-05-07
+Author: Xuan Khoa Tu Nguyen (ngxktuzkai2000@gmail.com)
+=end
+
+### 最大切分乘积：贪心 ###
+def max_product_cutting(n)
+  # 当 n <= 3 时，必须切分出一个 1
+  return 1 * (n - 1) if n <= 3
+  # 贪心地切分出 3 ，a 为 3 的个数，b 为余数
+  a, b = n / 3, n % 3
+  # 当余数为 1 时，将一对 1 * 3 转化为 2 * 2
+  return (3.pow(a - 1) * 2 * 2).to_i if b == 1
+  # 当余数为 2 时，不做处理
+  return (3.pow(a) * 2).to_i if b == 2
+  # 当余数为 0 时，不做处理
+  3.pow(a).to_i
+end
+
+### Driver Code ###
+if __FILE__ == $0
+  n = 58
+
+  # 贪心算法
+  res = max_product_cutting(n)
+  puts "最大切分乘积为 #{res}"
+end