string-to-integer.rb

# Implement the myAtoi(string s) function, which converts a string to a 32-bit signed integer.

# The algorithm for myAtoi(string s) is as follows:

#     Whitespace: Ignore any leading whitespace (" ").
#     Signedness: Determine the sign by checking if the next character is '-' or '+', assuming positivity if neither present.
#     Conversion: Read the integer by skipping leading zeros until a non-digit character is encountered or the end of the string is reached. If no digits were read, then the result is 0.
#     Rounding: If the integer is out of the 32-bit signed integer range [-231, 231 - 1], then round the integer to remain in the range. Specifically, integers less than -231 should be rounded to -231, and integers greater than 231 - 1 should be rounded to 231 - 1.

# Return the integer as the final result.

 

# Example 1:

# Input: s = "42"

# Output: 42

# Explanation:

# The underlined characters are what is read in and the caret is the current reader position.
# Step 1: "42" (no characters read because there is no leading whitespace)
#          ^
# Step 2: "42" (no characters read because there is neither a '-' nor '+')
#          ^
# Step 3: "42" ("42" is read in)
#            ^

# Example 2:

# Input: s = " -042"

# Output: -42

# Explanation:

# Step 1: "   -042" (leading whitespace is read and ignored)
#             ^
# Step 2: "   -042" ('-' is read, so the result should be negative)
#              ^
# Step 3: "   -042" ("042" is read in, leading zeros ignored in the result)
#                ^

# Example 3:

# Input: s = "1337c0d3"

# Output: 1337

# Explanation:

# Step 1: "1337c0d3" (no characters read because there is no leading whitespace)
#          ^
# Step 2: "1337c0d3" (no characters read because there is neither a '-' nor '+')
#          ^
# Step 3: "1337c0d3" ("1337" is read in; reading stops because the next character is a non-digit)
#              ^

# Example 4:

# Input: s = "0-1"

# Output: 0

# Explanation:

# Step 1: "0-1" (no characters read because there is no leading whitespace)
#          ^
# Step 2: "0-1" (no characters read because there is neither a '-' nor '+')
#          ^
# Step 3: "0-1" ("0" is read in; reading stops because the next character is a non-digit)
#           ^

# Example 5:

# Input: s = "words and 987"

# Output: 0

# Explanation:

# Reading stops at the first non-digit character 'w'.

 

# Constraints:

#     0 <= s.length <= 200
#     s consists of English letters (lower-case and upper-case), digits (0-9), ' ', '+', '-', and '.'.

# @param {String} s
# @return {Integer}
def my_atoi(s)
  min_value, max_value = -2**31, 2**31 -1
  valid_signs = ['-','+']
  input_chars = s.strip.split('')
  valid_chars = []
  mult = input_chars[0] == '-' ? -1 : 1
  input_chars.shift if valid_signs.include?(input_chars[0])
  
  input_chars.each do |c|
      break unless c.between?('0','9')

      valid_chars << c
  end

  return 0 if valid_chars.empty?

  result = valid_chars.join.to_i * mult
  result = min_value if result < min_value
  result = max_value if result > max_value 

  result
  
end