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Python Program to Find the Number Occurring Odd Number of Times

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  • Last Updated : 22 Jun, 2022

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 : arr = {1, 2, 3, 2, 3, 1, 3}
Output : 3

Input : arr = {5, 7, 2, 7, 5, 2, 5}
Output : 5

Recommended: Please solve it on “PRACTICE ” first, before moving on to the solution.

Python3




# Python program to find the element occurring
# odd number of times
     
# function to find the element occurring odd
# number of times
def getOddOccurrence(arr, arr_size):
     
    for i in range(0, arr_size):
        count = 0
        for j in range(0, arr_size):
            if arr[i] == arr[j]:
                count+= 1
             
        if (count % 2 != 0):
            return arr[i]
         
    return -1
     
     
# driver code
arr = [2, 3, 5, 4, 5, 2, 4, 3, 5, 2, 4, 4, 2 ]
n = len(arr)
print(getOddOccurrence(arr, n))
 
# This code has been contributed by
# Smitha Dinesh Semwal

Output:

5

Time Complexity : O(n^2)
Auxiliary Space: O(1)

A Better Solution is to use Hashing. Use array elements as key and their counts as value. Create an empty hash table. One by one traverse the given array elements and store counts. Time complexity of this solution is O(n). But it requires extra space for hashing.

Program :

Python




# Python program to find the element occurring odd number of times
 
def getOddOccurrence(arr):
 
    # Initialize result
    res = 0
     
    # Traverse the array
    for element in arr:
        # XOR with the result
        res = res ^ element
 
    return res
 
# Test array
arr = [ 2, 3, 5, 4, 5, 2, 4, 3, 5, 2, 4, 4, 2]
 
print "% d" % getOddOccurrence(arr)

Output:

5

Time Complexity : O(n)
Auxiliary Space: O(n)

Please refer complete article on Find the Number Occurring Odd Number of Times for more details!


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