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Python program to find common elements in three lists using sets
  • Last Updated : 26 Oct, 2018

Prerequisite : Sets in Python

Given three arrays, we have to find common elements in three sorted lists using sets.

Examples :

Input : ar1 = [1, 5, 10, 20, 40, 80]
        ar2 = [6, 7, 20, 80, 100]
        ar3 = [3, 4, 15, 20, 30, 70, 80, 120]

Output : [80, 20]

Input : ar1 = [1, 5, 5]
        ar2 = [3, 4, 5, 5, 10]
        ar3 = [5, 5, 10, 20]

Output : [5]

Approach :
We have given three arrays, with the help of sets one can easily find out the intersection of these Arrays.



Intersection method simply provides the intersection of both the arrays upon which you want to perform the operation of intersection (or, it simply gives out the common elements in both the array). We will be taking three arrays and then we will take out the intersection.

Below is the implementation of above approach :

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# Python3 program to find common elements 
# in three lists using sets
  
def IntersecOfSets(arr1, arr2, arr3):
    # Converting the arrays into sets
    s1 = set(arr1)
    s2 = set(arr2)
    s3 = set(arr3)
      
    # Calculates intersection of 
    # sets on s1 and s2
    set1 = s1.intersection(s2)         #[80, 20, 100]
      
    # Calculates intersection of sets
    # on set1 and s3
    result_set = set1.intersection(s3)
      
    # Converts resulting set to list
    final_list = list(result_set)
    print(final_list)
  
# Driver Code
if __name__ == '__main__' :
      
    # Elements in Array1
    arr1 = [1, 5, 10, 20, 40, 80, 100]
      
    # Elements in Array2
    arr2 = [6, 7, 20, 80, 100]
      
    # Elements in Array3
    arr3 = [3, 4, 15, 20, 30, 70, 80, 120]
      
    # Calling Function
    IntersecOfSets(arr1, arr2, arr3)

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Output :

[80, 20]

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