Bug fixes and improvements (#1380)

* preorder, inorder, postorder -> pre-order, in-order, post-order

* Bug fixes

* Bug fixes

* Update what_is_dsa.md

* Sync zh and zh-hant versions

* Sync zh and zh-hant versions.

* Update performance_evaluation.md and time_complexity.md

* Add @khoaxuantu to the landing page.

* Sync zh and zh-hant versions

* Add @ khoaxuantu to the landing page of zh-hant and en versions.

zh-hant/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
+
+### 零錢兌換：貪婪 ###
+def coin_change_greedy(coins, amt)
+  # 假設 coins 串列有序
+  i = coins.length - 1
+  count = 0
+  # 迴圈進行貪婪選擇，直到無剩餘金額
+  while amt > 0
+    # 找到小於且最接近剩餘金額的硬幣
+    while i > 0 && coins[i] > amt
+      i -= 1
+    end
+    # 選擇 coins[i]
+    amt -= coins[i]
+    count += 1
+  end
+  # 若未找到可行方案， 則返回 -1
+  amt == 0 ? count : -1
+end
+
+### Driver Code ###
+if __FILE__ == $0
+  # 貪婪：能夠保證找到全域性最優解
+  coins = [1, 5, 10, 20, 50, 100]
+  amt = 186
+  res = coin_change_greedy(coins, amt)
+  puts "\ncoins = #{coins}, amt = #{amt}"
+  puts "湊到 #{amt} 所需的最少硬幣數量為 #{res}"
+
+  # 貪婪：無法保證找到全域性最優解
+  coins = [1, 20, 50]
+  amt = 60
+  res = coin_change_greedy(coins, amt)
+  puts "\ncoins = #{coins}, amt = #{amt}"
+  puts "湊到 #{amt} 所需的最少硬幣數量為 #{res}"
+  puts "實際上需要的最少數量為 3 , 即 20 + 20 + 20"
+
+  # 貪婪：無法保證找到全域性最優解
+  coins = [1, 49, 50]
+  amt = 98
+  res = coin_change_greedy(coins, amt)
+  puts "\ncoins = #{coins}, amt = #{amt}"
+  puts "湊到 #{amt} 所需的最少硬幣數量為 #{res}"
+  puts "實際上需要的最少數量為 2 , 即 49 + 49"
+end