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Python | Reverse sign of each element in given list

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  • Last Updated : 23 Jan, 2023
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Given a list of integers, write a Python program to reverse the sign of each element in given list. Examples:

Input : [-1, 2, 3, -4, 5, -6, -7]
Output : [1, -2, -3, 4, -5, 6, 7]

Input : [-5, 9, -23, -2, 7]
Output : [5, -9, 23, 2, -7]

Methods #1: List comprehension 

Python3




# Python3 program to Convert positive
# list integers to negative and vice-versa
def Convert(lst):
    return [ -i for i in lst ]
 
# Driver code
lst = [-1, 2, 3, -4, 5, -6, -7]
print(Convert(lst))

Output:

[1, -2, -3, 4, -5, 6, 7]

Time Complexity: O(n).

Space Complexity: O(1).
 

Methods #2 : Using numpy 

The Python module, Numpy, can also be used which is the most pythonic way to solve the given problem. The list is first converted to numpy array and then, the negative of the array is returned, which is finally converted to list. 

Python3




# Python3 program to Convert positive
# list integers to negative and vice-versa
import numpy as np
 
 
def Convert(lst):
    lst = np.array(lst)
    return list(-lst)
 
 
# Driver code
lst = [-1, 2, 3, -4, 5, -6, -7]
print(Convert(lst))

Output:

[1, -2, -3, 4, -5, 6, 7]

Time Complexity: O(n).

Space Complexity: O(1).

Method #3 : Using startswith() and replace() methods

Python3




# Python3 program to Convert positive
# list integers to negative and vice-versa
 
lst = [-1, 2, 3, -4, 5, -6, -7]
nl = list(map(str, lst))
res = []
for i in nl:
    if(i.startswith("-")):
        i = i.replace("-", "")
        res.append(int(i))
    else:
        i = "-"+i
        res.append(int(i))
print(res)

Output

[1, -2, -3, 4, -5, 6, 7]

Time Complexity: O(n).

Space Complexity: O(n).

Method #4: Using map function and neg operator methods

Python




# Python3 program to Convert positive
# list integers to negative and vice-versa
from operator import neg
lst = [-1, 2, 3, -4, 5, -6, -7]
nl = list(map(neg, lst))
print(nl)

Output:

[1, -2, -3, 4, -5, 6, 7]

Time Complexity: O(n).

Space Complexity: O(1).


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