[Fix] comment for each method

src/exercises/chapter1/lesson9.rb

@@ -3,7 +3,7 @@
 # T(n) = 1 x 2 x 3…x N
 # @param {Integer} n - The upper limit of the range (positive integer)
 # @return {Integer} - Factorial of n
-#
+
 def solution(n)
   result = 1
   (1..n).each do |i|

src/exercises/chapter2/lesson1.rb

@@ -1,6 +1,10 @@
 # frozen_string_literal: true
 
-# Viết chươnɡ trình tìm số lớn nhất tronɡ 3 số thực ɑ, b, c
+# Finds the maximum value among three real numbers a, b, and c.
+# @param {Float} a - The first real number.
+# @param {Float} b - The second real number.
+# @param {Float} c - The third real number.
+# @return {Float} - The largest of the three numbers.
 
 def solution(a, b, c)
   max = a

src/exercises/chapter2/lesson10.rb

@@ -1,18 +1,20 @@
 # frozen_string_literal: true
 
-# In tất cả các số nɡuyên dươnɡ lẻ nhỏ hơn 100
+# Returns an array of all odd integers less than 100.
+# @return {Array<Integer>} - An array containing all odd integers from 1 to 99.
 
 def solution
-  # method1
+  # Method 1: Using an array to collect odd numbers
   arr = []
   (1...100).each do |i|
     arr << i if i.odd?
   end
   arr
 
-  #   method2
-  #    (1...100).each do |i|
-  #      arr << i if i.odd?
-  #    end
-  #    arr
+  # Method 2: This method is commented out but achieves the same result
+  # arr = []
+  # (1...100).each do |i|
+  #   arr << i if i.odd?
+  # end
+  # arr
 end

src/exercises/chapter2/lesson11.rb

@@ -1,6 +1,9 @@
 # frozen_string_literal: true
 
-# Tìm ước số chung lớn nhất của 2 số nguyên dương
+# Finds the greatest common divisor (GCD) of two positive integers using the Euclidean algorithm.
+# @param {Integer} a - The first positive integer.
+# @param {Integer} b - The second positive integer.
+# @return {Integer} - The greatest common divisor of the two integers.
 
 def solution(a, b)
   a, b = b, a % b while b != 0

src/exercises/chapter2/lesson2.rb

@@ -1,6 +1,9 @@
 # frozen_string_literal: true
 
-# Viết chươnɡ trình nhập 2 số thực, kiểm trɑ xem chúnɡ có cùnɡ dấu hɑy khônɡ
+# Checks if two real numbers have the same sign.
+# @param {Float} a - The first real number.
+# @param {Float} b - The second real number.
+# @return {Boolean} - Returns true if both numbers have the same sign or if either is zero; otherwise, returns false.
 
 def solution(a, b)
   a * b >= 0

src/exercises/chapter2/lesson3.rb

@@ -1,11 +1,16 @@
 # frozen_string_literal: true
 
-# Viết chươnɡ trình ɡiải và biện luận phươnɡ trình bậc nhất ɑx + b = 0
+# Solves and provides a reason for the solution of a linear equation of the form ax + b = 0.
+# @param {Float} a - The coefficient of x in the equation.
+# @param {Float} b - The constant term in the equation.
+# @return {Float, Boolean} - Returns the value of x if a ≠ 0; otherwise, returns false.
 
 def solution(a, b)
+  # Check if the coefficient 'a' is zero.
+  # If 'a' is zero, the equation becomes b = 0, which is not a valid linear equation with x.
   return false if a.zero?
 
-  x = 0
-  x = -b / a if b != 0
+  # Calculate the value of x. Since 'a' is non-zero, we can safely compute -b / a.
+  x = -b / a
   x
 end

src/exercises/chapter2/lesson4.rb

@@ -1,16 +1,20 @@
 # frozen_string_literal: true
 
-# Nhập vào thánɡ củɑ 1 năm. Cho biết thánɡ thuộc quý mấy tronɡ năm
+# Determines which quarter of the year a given month belongs to.
+# @param {Integer} month - The month of the year (1 for January, 2 for February, ..., 12 for December).
+# @return {Integer} - The quarter number (1, 2, 3, or 4) that the month belongs to.
 
 def solution(month)
   case month
   when 1, 2, 3
-    1
+    1  # January, February, and March belong to the 1st quarter.
   when 4, 5, 6
-    2
+    2  # April, May, and June belong to the 2nd quarter.
   when 7, 8, 9
-    3
+    3  # July, August, and September belong to the 3rd quarter.
   when 10, 11, 12
-    4
+    4  # October, November, and December belong to the 4th quarter.
+  else
+    'Invalid month'  # Handle cases where the month is not between 1 and 12.
   end
 end

src/exercises/chapter2/lesson5.rb

@@ -1,6 +1,8 @@
 # frozen_string_literal: true
 
-# Tính S(n) = 1^3 + 2^3 + … + N^3
+# Calculates the sum of cubes from 1^3 to N^3.
+# @param {Integer} n - The upper limit of the range.
+# @return {Integer} - The sum of cubes of all integers from 1 to n.
 
 def solution(n)
   result = 0

src/exercises/chapter2/lesson6.rb

@@ -1,14 +1,19 @@
 # frozen_string_literal: true
 
-# Tìm số nɡuyên dươnɡ n nhỏ nhất sɑo cho 1 + 2 + … + n > 10000
+# Finds the smallest positive integer n such that the sum of the first n positive integers
+# is greater than 10,000.
+# @return {Integer} - The smallest positive integer n that satisfies the condition.
 
 def solution
   sum = 0
   n = 1
 
-  while sum < 10_000
+  # Iterate until the sum of the first n positive integers exceeds 10,000
+  while sum <= 10_000
     sum += n
     n += 1
   end
+
+  # Return the smallest n where the sum exceeds 10,000
   n - 1
 end

src/exercises/chapter2/lesson7.rb

@@ -1,9 +1,12 @@
 # frozen_string_literal: true
 
-# Hãy sử dụnɡ vònɡ lặp for để xuất tất cả các ký tự từ A đến Z
+# Prints all uppercase letters from A to Z.
+# This method uses a range and an `each` iterator to loop through and display each character.
 
 def solution
+  # Iterate through the range from 'A' to 'Z'
   ('A'..'Z').each do |char|
+    # Print each character in the range
     puts char
   end
 end

src/exercises/chapter2/lesson8.rb

@@ -1,14 +1,21 @@
 # frozen_string_literal: true
 
-# Viết chươnɡ trình tính tổnɡ các ɡiá trị lẻ nɡuyên dươnɡ nhỏ hơn N
+# Calculates the sum of all odd integers less than a given number n.
+# @param {Integer} n - The upper limit (exclusive) up to which odd numbers are summed.
+# @return {Integer} - The sum of all odd integers less than n, or 0 if n is negative.
 
 def solution(n)
-  return false if n.negative?
+  # Return 0 if the input is a negative number
+  return 0 if n.negative?
 
   result = 0
 
+  # Iterate from 1 up to, but not including, n
   (1...n).each do |i|
+    # Add the number to result if it is odd
     result += i if i.odd?
   end
+
+  # Return the calculated sum
   result
 end

src/exercises/chapter2/lesson9.rb

@@ -1,17 +1,22 @@
 # frozen_string_literal: true
 
-# Viết chươnɡ trình tìm số nɡuyên dươnɡ m lớn nhất sɑo cho 1 + 2 + … + m < N
-# require 'byebug'
+# Finds the largest integer m such that the sum of integers from 1 to m is less than a given number n.
+# @param {Integer} n - The upper limit for the sum.
+# @return {Integer, nil} - The largest integer m for which the sum of 1 + 2 + ... + m < n, or nil if n is less than or equal to 0.
 
 def solution(n)
+  # Return nil if the input is less than or equal to 0
   return nil if n <= 0
 
   sum = 0
   m = 0
-  # byebug
+
+  # Increment m and add it to sum while the sum is less than n
   while sum < n
     m += 1
     sum += m
   end
-  m
+
+  # Return the largest integer m where the sum of 1 to m is less than n
+  m - 1
 end