Python | Reverse sign of each element in given list

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).

Method #5 : Using find(),int()+slicing

Approach

Convert integer list to string list using list(),map(),str

1. Initiate a for loop to traverse string list
2. For each string if there is – sign at the beginning slice string 1 to end , convert it to integer and append to output list
3. If not append – sign at the beginning, convert to integer and append to output list
4. Display output list

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.find("-")==0):
        res.append(int(i[1:]))
    else:
        i = "-"+i
        res.append(int(i))
print(res)

Output

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

Time Complexity : O(N) N – number of elements in list

Auxiliary Space : O(N) N – number of elements in list