Add exercise 16~25

Author: ihower

16-array-sum.rb

@@ -0,0 +1,11 @@
+# 给定一阵列内含数字，输出最大值
+
+def find_max(array)
+  #....
+end
+
+arr = [8, 12, 36, 53, 9, 75, 3, 71, 59, 88]
+
+max = find_max(arr)
+puts "Max is #{max}" # 应该是 88
+

17-array-stats.rb

@@ -0,0 +1,20 @@
+# 使用者不断输入数字存进 Array，最后输出总和、平均、最大值、最小值
+
+arr = []
+
+while (true)
+  print "请输入数字，结束请直接按 Enter: "
+  user_input = gets
+  if user_input == "\n"
+    break
+  else
+    arr << user_input.to_i
+  end
+end
+
+puts arr.to_s
+
+puts "总和是 _____"
+puts "平均是 _____"
+puts "最大值是 _____"
+puts "最小值是 _____"

18-square.rb

@@ -0,0 +1,10 @@
+# 建构一个阵列有一百个的元素，内容是 0, 1, 4, 9, 16, 25...... 每个元素是该索引的平方
+
+arr = []
+
+print "请输入数字 N，然后按 Enter: "
+n = gets
+
+# ...
+
+puts arr.to_s

19-filter.rb

@@ -0,0 +1,9 @@
+# 给定一阵列内含数字，输出另一个数组只包含偶数
+
+def filter_even(arr)
+  #...
+end
+
+arr =  [7, 68, 42, 46, 9, 91, 77, 46, 86, 1]
+
+puts filter_even(arr).to_s # 应该是 [68, 42, 46, 46, 86]

20-sorting.rb

@@ -0,0 +1,11 @@
+# 承上题，请排序并去除重复的数字
+# Hint: 可用 arr.sort 排序，和 arr.uniq 去除重复
+
+def filter_even(arr)
+  #...
+end
+
+arr =  [7, 68, 42, 46, 9, 91, 77, 46, 86, 1]
+
+
+puts "________" # 应该是 [42, 46, 68, 86]

21-missing.rb

@@ -0,0 +1,9 @@
+# 给定一阵列内含数字，请输出 0~9 中不见的数字
+
+def find_missing(arr)
+  # ...
+end
+
+answer = find_missing( [2,2,1,5,8,4] )
+
+puts answer.to_s # 应该是 [0,3,6,7,9]

22-hash-max.rb

@@ -0,0 +1,19 @@
+# 给定一 Hash，输出有最大 value 的 key
+
+def find_max(hash)
+  # ...
+end
+
+h = {
+  "a" => 71,
+  "b" => 38,
+  "c" => 21,
+  "d" => 80,
+  "e" => 10
+}
+
+answer = find_max(h)
+
+puts "有最大 value 的是 #{answer}" # 应该是 d
+
+

23-hash-even.rb

@@ -0,0 +1,21 @@
+# 给定一 Hash，输出 value 是偶数的 keys
+
+def find_even_keys(hash)
+
+  # ... (请回传一个数组)
+
+end
+
+h = {
+  "a" => 71,
+  "b" => 38,
+  "c" => 21,
+  "d" => 80,
+  "e" => 10
+}
+
+answer = find_even_keys(h)
+
+puts "有偶数 value 的 keys 有 #{answer}" # 应该是数组 [b,d,e]
+
+

24-hash-count.rb

@@ -0,0 +1,18 @@
+# 计算一个阵列中各个元素的出现频率
+
+def count(arr)
+  h = {}
+
+  arr.each do |i|
+    # ...
+  end
+
+  return h # 回传一个 hash
+end
+
+arr =  ["a", "d", "d", "c", "b", "c", "c", "c", "d", "d", "e", "e", "e", "d", "a", "c", "e", "a", "d", "e"]
+
+answer = count(arr)
+
+puts answer # 答案应该是 {"a"=>3, "d"=>6, "c"=>5, "b"=>1, "e"=>5}
+

25-hash-filter.rb

@@ -0,0 +1,20 @@
+# 给定一个数组包含 Hash，请过滤和排序
+
+arr = [
+  { "name" => "Peter", "age" => 30 },
+  { "name" => "John", "age" => 15 },
+  { "name" => "David", "age" => 45 },
+  { "name" => "Steven", "age" => 22 },
+  { "name" => "Vincent", "age" => 6 },
+]
+
+# ....
+
+puts "所有成年人，并由小到大: _________"
+
+# 答案应该是
+#[
+#  { "name" => "Steven", "age" => 22 },
+#  { "name" => "Peter", "age" => 30 },
+#  { "name" => "David", "age" => 45 }
+#]