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Python | Increment 1’s in list based on pattern

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  • Last Updated : 30 Jul, 2019

Given a list of binary numbers 0 and 1, Write a Python program to transform the list in such a way that whenever 1 appears after the occurrence of a sequence of 0’s, increment it by n+1, where ‘n’ is the last increment.

Examples:

Input : [0, 1, 0, 0, 1, 1, 0, 0, 0, 1, 1, 1]
Output : [0, 1, 0, 0, 2, 2, 0, 0, 0, 3, 3, 3]

Input : [1, 0, 1, 0, 0, 0, 1, 1, 0, 0, 1, 1, 1, 0, 1, 0, 1]
Output : [1, 0, 2, 0, 0, 0, 3, 3, 0, 0, 4, 4, 4, 0, 5, 0, 6]

 
Approach #1 : Naive Approach

This is a naive approach to the given problem. It uses two variable ‘previous’ and ‘grp’ to store previously incremented number and to store the number of 1’s in a group. Now, using a for loop, increment 1’s accordingly.




# Python3 program to increment 1's in 
# list based on pattern 
  
def transform(lst):
      
    previous = 0
    grp = 0
    for elem in lst:
        if elem and not previous:
             grp += 1
        previous = elem
        yield (grp if elem else 0)
      
# Driver code
lst = [0, 1, 0, 0, 1, 1, 0, 0, 0, 1, 1, 1]
x = (transform(lst))
res = []
for i in range(0, len(lst)):
    res.append(next(x))
print(res)


Output:

[0, 1, 0, 0, 2, 2, 0, 0, 0, 3, 3, 3]

 

Approach #2 : Using count, chain and groupby from itertools module.
This is an efficient and more pythonic approach towards the given problem where we use count, chain and groupby from itertools module.




# Python3 program to increment 1's in 
# list based on pattern 
from itertools import * 
  
def transform(lst):
      
    c = count(1)
    return list(chain(*[list(g) if k != 1 else [next(c)]*len(list(g)) 
    for k, g in groupby(lst)]))
      
# Driver code
lst = [0, 1, 0, 0, 1, 1, 0, 0, 0, 1, 1, 1]
print(transform(lst))


Output:

[0, 1, 0, 0, 2, 2, 0, 0, 0, 3, 3, 3]

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