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

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)

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