Python | Check if given string can be formed by concatenating string elements of list

Given a string ‘str’ and a list of string elements, write a Python program to check whether given string can be formed by concatenating the string elements of list or not. 

Examples:

Input : str = 'python'
        lst = ['co', 'de', 'py', 'ks', 'on']
Output : False

Input : str = 'geeks'
        lst = ['for', 'ge', 'abc', 'ks', 'e', 'xyz']
Output : True

Approach #1 : Using itertools.permutations

We can use all the permutations of the given list and then perform join operation on them. If any join result is equal to the given string, return true, otherwise false.  

Python3

# Python3 program to Check if given string can
# be formed by concatenating string elements
# of list
from itertools import permutations

def checkList(str, lst):
    for i in range(2, len(lst)+1):
        for perm in permutations(lst, i):
            if ''.join(perm)== str:
                return True

    return False

# Driver code
str = 'geeks'
lst = ['for', 'ge', 'abc', 'ks', 'e', 'xyz']
print(checkList(str, lst))

Output:

True

Approach #2 : Python RegEx

Python3

# Python3 program to Check if given string can
# be formed by concatenating string elements
# of list
import re

def checkList(str, lst):

    r = re.compile("(?:" + "|".join(lst) + ")*$")
    if r.match(str) != None:
        return True

    return False

# Driver code
str = 'geeks'
lst = ['for', 'ge', 'abc', 'ks', 'e']
print(checkList(str, lst))

Output:

True

Approach#3: Using String.replace() and loop: We iterate over the list element by element and remove that element in string. After all Iteration if string become empty then it can be form by using list of string else is cannot. 

Python3

# Python3 program to Check if given string can
# be formed by concatenating string elements
# of list

# Function to check string can be formed using list or not
def checkList(str1, list1):
    # Iterating over list of string
    for i in list1:
        # Replacing the sub-string from string
        str1 = str1.replace(i, "")
        # Checking the emptiness of string
        if str1 == "":
            return True

    # Else returning False
    else: return False

# Driver code
str = 'geeks'
lst = ['for', 'ge', 'abc', 'e', 'ks', 'xyz']
print(checkList(str, lst))

Output:

True