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Python | Find the Number Occurring Odd Number of Times using Lambda expression and reduce function

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Given an array of positive integers. All numbers occur even number of times except one number which occurs odd number of times. Find the number in O(n) time & constant space. Examples:

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

We have existing solution for this problem please refer Find the Number Occurring Odd Number of Times link. we will solve this problem in python quickly using Reduce(expression, iterable) method. 

Python3

# Python program to Find the Number
# Occurring Odd Number of Times
# using Lambda expression and reduce function
 
from functools import reduce
 
def oddTimes(input):
     # write lambda expression and apply
     # reduce function over input list
     # until single value is left
     # expression reduces value of a ^ b into single value
     # a starts from 0 and b from 1
     # ((((((1 ^ 2)^3)^2)^3)^1)^3)
     print (reduce(lambda a, b: a ^ b, input))
 
# Driver program
if __name__ == "__main__":
    input = [1, 2, 3, 2, 3, 1, 3]
    oddTimes(input)

                    

Output:

3

Time complexity: O(n)
Auxiliary space: O(1)


Last Updated : 26 Feb, 2023
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