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)) |
[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)) |
[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) |
[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
- Initiate a for loop to traverse string list
- For each string if there is – sign at the beginning slice string 1 to end , convert it to integer and append to output list
- If not append – sign at the beginning, convert to integer and append to output list
- 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) |
[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
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