Given a list of integers, write a Python program to convert the given list into a single integer.
Examples:
1 2 3 4 5 6 7 8 9 10 
<strong>Input :</strong> [1, 2, 3] <strong>Output </strong>: 123 <strong>Input :</strong> [55, 32, 890] <strong>Output :</strong> 5532890 
There are multiple approaches possible to convert the given list into a single integer. Let’s see each one by one.
Approach #1 : Naive Method
Simply iterate each element in the list and print them without space in between.

Output:
1 2 3 4 5 
121517 
Approach #2 : Using join()
Use the join()
method of Python. First convert the list of integer into a list of strings( as join()
works with strings only). Then, simply join them using join()
method. It takes a time complexity of O(n)
.

Output:
1 2 3 4 5 
123 
Approach #3 : Using map()
Another approach to convert a list of multiple integers into a single integer is to use map()
function of Python with str function to convert the Integer list to string list. After this, join them on the empty string and then cast back to integer.

Output:
1 2 3 4 5 
123 
Approach #4 : Multiplying by corresponding power of 10
A more mathematical way, which does not require to convert the integer list to string list is, to multiply each integer element with its corresponding power of 10, and then summing it up. It takes a time complexity of O(n)
.

Output:
1 2 3 4 5 
123 
A small variation to this program leads to less computation in calculation of sum, i.e. using reduce()
. This makes use of Horner’s rule, which factors the polynomial representing the number to reduce the number of multiplications.

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