Print all Substrings of length n possible from the given String – GeeksforGeeks

Given a string str and an integer N, the task is to print all possible sub-strings of length N.

Examples:

Input: str = “geeksforgeeks”, N = 3
Output: gee eek eks ksf sfo for org rge gee eek eks
Explanations: All possible sub-strings of length 3 are “gee”, “eek”, “eks”, “ksf”, “sfo”, “for”, “org”, “rge”, “gee”, “eek” and “eks”.

Input: str = “GFG”, N = 2 
Output: GF FG
Explanations: All possible sub-strings of length 2 are “GF”, “FG”

Method 1: Using slicing

Approach: To solve the problem follow the below steps:

• Initialize a variable ‘n’ to the desired length of the substrings.
• Use a for loop to iterate through the characters of the original string, starting from the first character.
• In each iteration of the loop, use slicing to extract a substring of length ‘n’ from the original string, starting from the current character. The slicing can be done by using the syntax ‘string[start:end]’ where the start and end are the indices of the first and last character of the substring, respectively.
• In each iteration, the variable ‘i’ will be the starting index of the substring, and ‘i + n’ will be the ending index of the substring, so the substring can be extracted by using the slicing syntax ‘string[i: i + n]’.
• Print or store the extracted substring for further processing.
• Repeat the process for all characters in the original string.

Below is the implementation of the above approach:

gee eek eks ksf sfo for org rge gee eek eks 

Time Complexity: O(|str|*n), where |str| is the length of the string
Auxiliary Space: O(n)

Method 2: Using a for loop

Approach: To solve the problem follow the below steps:

• Initialize a variable ‘n‘ to the desired length of the substrings.
• Use a for loop to iterate through the characters of the original string, starting from the first character.
• In each iteration of the outer loop, initialize an empty variable ‘substring‘ to store the extracted substring.
• Use a nested for loop to iterate through the next ‘n’ characters of the original string, starting from the current character.
• In each iteration of the inner loop, add the current character to the ‘substring’ variable.
• After the inner loop finishes, print or store the extracted substring for further processing.
• Repeat the process for all characters in the original string.

Below is the implementation of the above approach:

gee eek eks ksf sfo for org rge gee eek eks 

Time Complexity: O(|str|*n), where |str| is the length of the string
Auxiliary Space: O(n)

Method 3: Using list comprehension (Only for Python)

Approach: To solve the problem follow the below steps:

• Initialize a variable ‘n’ to the desired length of the substrings.
• Use a list comprehension to iterate through the characters of the original string and extract substrings of length ‘n’ in one line.
• The list comprehension uses the slicing syntax ‘string[start:end]’ where the start and end are the indices of the first and last character of the substring, respectively.
• The variable ‘i’ will be the starting index of the substring and ‘i+n’ will be the ending index of the substring, so the substring can be extracted by using the slicing syntax ‘string[i:i+n]’ inside the list comprehension.
• Assign the output of the list comprehension to a variable e.g. substrings = [string[i:i+n] for i in range(len(string) – n + 1)]
• Then you can print or access individual substrings from the list by indexing.

Below is the implementation of the above approach:

['gee', 'eek', 'eks', 'ksf', 'sfo', 'for', 'org', 'rge', 'gee', 'eek', 'eks']

Time Complexity: O(|str|*n), where |str| is the length of the string
Auxiliary Space: O(|str|*n)

N.B.: It is important to note that the above approach will only work if the length of the string is greater than n, otherwise it will throw index out of range error.