Python program to remove last N characters from a string

Given a string S and an integer N, the task is to remove N characters from the end of the string S.

Input: S = “GeeksForGeeks”, N = 5
Output: GeeksFor
Explanation: Removing the last 5 characters from “GeeksForGeeks” modifies the string to “GeeksFor”.

Input: S = “Welcome”, N = 3
Output: Welc

Approach 1: Follow the steps below to solve the problem:

• Initialize an empty string, say res, to store the resultant string.
• Iterate over the characters of the string S up to index len(S) – N.
• Keep inserting the encountered characters into res.

Below is the implementation of the above approach:

Python3

# Python3 code for the above approach

# Function to remove last N
# characters from string
def removeLastN(S, N):

    # Stores the resultant string
    res = ''

    # Traverse the string
    for i in range(len(S)-N):

          # Insert current character
        res += S[i]

    # Return the string
    return res



# Driver Code

# Input
S = "GeeksForGeeks"
N = 5

print(removeLastN(S, N))

Output:

GeeksFor

Time Complexity: O(N), where N is the length of the string.
Auxiliary Space: O(N)

Approach 2: This problem can be solved using replace(). Follow the steps below to solve the problem:

1. Initialize a string, say res, to store the resultant string.
2. Reverse the string S.
3. Using replace() method, remove the first occurrence of the first N characters of S and store it in res.
4. Reverse the string res.

Below is the implementation of the above approach:

Python3

# Python3 code for the above approach

# Function to remove last N
# characters from string S
def removeLastN(S, N):

    # Stores resultant string
    res = ''

    # Reversing S
    S = S[::-1]

    # Removing last N characters
    res = S.replace(S[:N], '', 1)

    # Reversing back res
    res = res[::-1]

    # Return the string
    return res

# Driver Code

# Input
S = "GeeksForGeeks"
N = 5

print(removeLastN(S, N))

Output:

GeeksFor

Time Complexity: O(N), where N is the length of the string.
Auxiliary Space: O(N)

String slicing-based Approach: Follow the steps below to solve the problem:

• Initialize a string, say res, to store the resultant string.
• Update res to S[:len(S) – N], to store all characters except the last N characters of S.

Below is the implementation of the above approach:

Python3

# Python3 code for the above approach

# Function to remove last N
# characters from string S
def removeLastN(S, N):

    S = S[:len(S)-N]

    # Return the string
    return S

# Driver Code

# Input
S = "GeeksForGeeks"
N = 5

print(removeLastN(S, N))

Output:

GeeksFor

Time Complexity: O(N), where N is the length of the string.
Auxiliary Space: O(1)