Python Program to Group Strings by K length Using Suffix

Given Strings List, the task is to write a Python program to group them into K-length suffixes.

Input : test_list = [“food”, “peak”, “geek”, “good”, “weak”, “sneek”], K = 3 
Output : {‘ood’: [‘food’, ‘good’], ‘eak’: [‘peak’, ‘weak’], ‘eek’: [‘geek’, ‘sneek’]} 
Explanation : words ending with ood are food and good, hence grouped.

Input : test_list = [“peak”, “geek”, “good”, “weak”], K = 3 
Output : {‘ood’: [‘good’], ‘eak’: [‘peak’, ‘weak’], ‘eek’: [‘geek’]} 
Explanation : word ending with ood is good, hence grouped. 

Method 1 : Using try/except + loop

In this, we extract the last K characters and form a string, and append it to the existing key’s list corresponding to it, if not found, it goes through catch flow and creates a new key with a list with the first word initialized.

Python3

# Python3 code to demonstrate working of
# Group Strings by K length Suffix
# Using try/except + loop

# initializing list
test_list = ["food", "peak", "geek",
             "good", "weak", "sneek"]

# printing original list
print("The original list is : " + str(test_list))

# initializing K
K = 3

res = {}
for ele in test_list:

    # extracting suffix
    suff = ele[-K : ]

    # appending if key found, else creating new one
    try:
        res[suff].append(ele)
    except:
        res[suff] = [ele]

# printing result
print("The grouped suffix Strings : " + str(res))

Output

The original list is : ['food', 'peak', 'geek', 'good', 'weak', 'sneek']
The grouped suffix Strings : {'ood': ['food', 'good'], 'eak': ['peak', 'weak'], 'eek': ['geek', 'sneek']}

Time Complexity: O(n)
Auxiliary Space: O(n)

Method 2 : Using defaultdict() + loop.

This method avoids the need of using try/except block as default list initialization is handled by defaultdict().

Python3

# Python3 code to demonstrate working of
# Group Strings by K length Suffix
# Using defaultdict() + loop
from collections import defaultdict

# initializing list
test_list = ["food", "peak", "geek",
             "good", "weak", "sneek"]

# printing original list
print("The original list is : " + str(test_list))

# initializing K
K = 3

res = defaultdict(list)
for ele in test_list:

    # extracting suffix
    suff = ele[-K : ]

    # appending into matched suffix key
    res[suff].append(ele)

# printing result
print("The grouped suffix Strings : " + str(dict(res)))

Output

The original list is : ['food', 'peak', 'geek', 'good', 'weak', 'sneek']
The grouped suffix Strings : {'ood': ['food', 'good'], 'eak': ['peak', 'weak'], 'eek': ['geek', 'sneek']}

Time Complexity: O(n)
Auxiliary Space: O(n)