# Python program to find common elements in three lists using sets

Prerequisite : Sets in Python

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

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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 :

`# 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)` |

Output :

[80, 20]