Given a string. the task is to print numeric prefix in string (if it is present in string). Given below are few methods to solve the task.
Method #1: Using Naive Method
Python3
# Python code to demonstrate# to get numeric prefix in string# if present# initialising stringini_string = "123abcjw"ini_string2 = "abceddfgh"# printing string and its lengthprint ("initial string : ", ini_string, ini_string2)# code to find numeric prefix in stringres1 = ''.join(c for c in ini_string if c in '0123456789')res2 = ''.join(c for c in ini_string2 if c in '0123456789')# printing resultant stringprint ("first string result: ", str(res1))print ("second string result: ", str(res2)) |
initial string : 123abcjw abceddfgh first string result: 123 second string result:
Time Complexity: O(n + m), where n + m are the length of given strings
Auxiliary Space: O(n + m)
Method #2: Using takewhile
Python3
# Python code to demonstrate# to get numeric prefix in string# if presentfrom itertools import takewhile# initialising stringini_string = "123abcjw"ini_string2 = "abceddfgh"# printing string and its lengthprint ("initial string : ", ini_string, ini_string2)# code to find numeric prefix in stringres1 = ''.join(takewhile(str.isdigit, ini_string))res2 = ''.join(takewhile(str.isdigit, ini_string2))# printing resultant stringprint ("first string result: ", res1)print ("second string result: ", res2) |
initial string : 123abcjw abceddfgh first string result: 123 second string result:
Time complexity: O(n), where n is the length of the string, since the code uses a for loop to iterate through the string and calls the built-in method str.isdigit() for each character in the string.
Auxiliary space: O(m), where m is the length of the numeric prefix in the string.
Method #3: Using re.sub
Python3
# Python code to demonstrate# to get numeric prefix in string# if presentimport re# initialising stringini_string = "123abcjw"ini_string2 = "abceddfgh"# printing string and its lengthprint ("initial string : ", ini_string, ini_string2)# code to find numeric prefix in stringres1 = re.sub('\D.*', '', ini_string)res2 = re.sub('\D.*', '', ini_string2)# printing resultant stringprint ("first string result: ", str(res1))print ("second string result: ", str(res2)) |
initial string : 123abcjw abceddfgh first string result: 123 second string result:
Time Complexity: O(n), where n is the length of the string.
Auxiliary Space: O(1).
Using Method #4: Using re.findall
Python3
# Python code to demonstrate# to get numeric prefix in string# if presentimport re# initialising stringini_string = "123abcjw"ini_string2 = "abceddfgh"# printing string and its lengthprint ("initial string : ", ini_string, ini_string2)# code to find numeric prefix in stringres1 = ''.join(re.findall('\d+', ini_string))res2 = ''.join(re.findall('\d+', ini_string2))# printing resultant stringprint ("first string result: ", str(res1))print ("second string result: ", str(res2)) |
initial string : 123abcjw abceddfgh first string result: 123 second string result:
Time complexity: The time complexity of this program is O(n), where n is the length of the input string. The reason is that we perform a single pass over the string to extract the numeric prefix using the re.findall() function.
Auxiliary space: The auxiliary space used by this program is O(1), as we only use a few variables to store the input string, the regex pattern, and the extracted numeric prefix. The space used by these variables does not depend on the length of the input string. Therefore, the space complexity is constant.
Method #5: Using isalpha() method
Python3
# Python code to demonstrate# to get numeric prefix in string# if presentdef fun(s): x="" for i in s: if i.isalpha(): break else: x+=i return x# initialising stringini_string = "123abcjw"ini_string2 = "abceddfgh"# printing string and its lengthprint ("initial string : ", ini_string, ini_string2)# code to find numeric prefix in stringres1 = fun(ini_string)res2 = fun(ini_string2)# printing resultant stringprint ("first string result: ", res1)print ("second string result: ", res2) |
initial string : 123abcjw abceddfgh first string result: 123 second string result:
Time Complexity : O(N)
Auxiliary Space : O(N)
Method #6: Using re.search()
In the above code, we are using the search function from the re module to find the longest prefix of numeric characters in the input string. The regular expression r’^\d+’ matches one or more digits at the beginning of the string (the ^ symbol represents the start of the string).
If a match is found, the search function returns a Match object representing the match. We can use the group method of this object to extract the matched string. If no match is found, search returns None, and we return an empty string instead.
Finally, we use the print function to output the resulting prefix for each example input string.
Python
import redef get_numeric_prefix(s): """ Extracts the numeric prefix from a string. """ # Use a regular expression to match the longest prefix of numeric characters match = re.search(r'^\d+', s) if match: # Return the matched prefix return match.group() else: # If no match was found, return an empty string return ""# Example usageprint(get_numeric_prefix("123abcjw"))print(get_numeric_prefix("abceddfgh"))print(get_numeric_prefix("123abcjw12"))#This code is contributed by Edula Vinay Kumar Reddy |
123 123
Time Complexity O(n), where n is the length of the input string.
Auxiliary Space: O(n).
