Python | Minimum Sum of Consecutive Characters

Sometimes, we might have a problem in which we require to get the minimum sum of 2 numbers from list but with the constraint of having the numbers in successions. This type of problem can occur while competitive programming. Let’s discuss certain ways in which this problem can be solved.

Method #1: Using min() + zip() + list comprehension

This problem can be solved using the combination of the above three functions in which min function can be used to get the minimum value, zip, and list comprehension doing the task of extending the logic to the whole list. 

Python3

# Python3 code to demonstrate
# Minimum Sum of Consecutive Characters
# using zip() + min() + list comprehension

# initializing string
test_string = '6543452345456987653234'

# printing original string
print("The original string : " + str(test_string))

# using zip() + min() + list comprehension
# Minimum Sum of Consecutive Characters
test_string = list(test_string)
res = min(int(a) + int(b) for a, b in zip(test_string, test_string[1:]))

# print result
print("The minimum consecutive sum is : " + str(res))

Output : 

The original string : 6543452345456987653234
The minimum consecutive sum is : 5

Method #2 : Using min() + map() + operator.add

The above problem can also be solved using yet another combination of functions. In this combination, map functions performs the task of extending the logic to whole list and add operator is used to perform the multiplication. 

Python3

# Python3 code to demonstrate
# Minimum Sum of Consecutive Characters
# using min() + map() + operator.add
from operator import add

# initializing string
test_string = '6543452345456987653234'

# printing original string
print("The original string : " + str(test_string))

# using min() + map() + operator.add
# Minimum Sum of Consecutive Characters
res = min(map(add, map(int, test_string), map(int, test_string[1:])))

# print result
print("The minimum consecutive sum is : " + str(res))

Output : 

The original string : 6543452345456987653234
The minimum consecutive sum is : 5

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

Method 3: Using a for loop

• Initialize a variable min_sum to a large value, for example, float(‘inf’).
• Convert the input string into a list of integers using list comprehension and store it in a variable num_list.
• Iterate over the list num_list from the second element to the end using a for loop.
• Calculate the sum of the current element and the previous element using the index of the for loop.
• If the sum is less than min_sum, update min_sum to the sum.
• After the loop finishes, print the value of min_sum.

Example:

Python3

# Python3 code to demonstrate
# Minimum Sum of Consecutive Characters

# initializing string
test_string = '6543452345456987653234'

# printing original string
print("The original string : " + str(test_string))

# using for loop to find the minimum consecutive sum
min_sum = float('inf')
num_list = [int(x) for x in test_string]
for i in range(1, len(num_list)):
    curr_sum = num_list[i-1] + num_list[i]
    if curr_sum < min_sum:
        min_sum = curr_sum

# print result
print("The minimum consecutive sum is : " + str(min_sum))

Output

The original string : 6543452345456987653234
The minimum consecutive sum is : 5

Time complexity: O(n), where n is the length of the input string.
Auxiliary space: O(n), as we create a list of integers with the same length as the input string.

Method 4: Using itertools pairwise and min()

Python3

import itertools

# initializing string
test_string = '6543452345456987653234'

# printing original string
print("The original string : " + str(test_string))

# using itertools pairwise and min to find the minimum consecutive sum
num_list = [int(x) for x in test_string]
min_sum = min(a + b for a, b in itertools.pairwise(num_list))

# print result
print("The minimum consecutive sum is : " + str(min_sum))

Output

The original string : 6543452345456987653234
The minimum consecutive sum is : 5

Time complexity: O(n)
Auxiliary space: O(1) (excluding the space for the input string and the output message)

Method 5: Using a sliding window technique.

• Initialize the input string “test_string” to the value ‘6543452345456987653234’.
• Print the original string using the “print” function.
• Initialize a variable “min_sum” to infinity using the “float” function.
• Iterate over each pair of consecutive digits in the string using a “for” loop, where the loop variable “i” ranges from 0 to the length of the string minus 1.
• Within each iteration of the loop, compute the sum of the current digit and the next digit, and store it in the variable “window_sum”.
• Check if the “window_sum” is less than the current value of “min_sum”.
• If “window_sum” is less than “min_sum”, update the value of “min_sum” to be equal to “window_sum”.
• After iterating over all pairs of consecutive digits, print the minimum consecutive sum using the “print” function.

Python3

import re

# initializing string
test_string = '6543452345456987653234'

# printing original string
print("The original string : " + str(test_string))

# using sliding window technique to find the minimum consecutive sum
min_sum = float('inf')
for i in range(len(test_string)-1):
    window_sum = int(test_string[i]) + int(test_string[i+1])
    if window_sum < min_sum:
        min_sum = window_sum

# print result
print("The minimum consecutive sum is : " + str(min_sum))

Output

The original string : 6543452345456987653234
The minimum consecutive sum is : 5

Time complexity: O(n) where n is the length of the input string ‘test_string’.
Auxiliary space: O(1) as we are not using any extra data structure to store the window sum or the minimum sum seen so far.