# Python | Check if two lists have at least one element in common

Examples :

` Input: a = [1, 2, 3, 4, 5] b = [5, 6, 7, 8, 9] Output: True Input: a = [1, 2, 3, 4, 5] b = [6, 7, 8, 9] Output: False `

Method 1: bypass list

By using traversal on two lists, we can check if there is at least one common element in them. When traversing two lists, if we find one element in common, we return true. After a full traversal and validation, if the elements don’t match, we return false.

 ` # Python program to check ` ` # if two lists have at least ` ` # one element in common ` ` # use a bypass list `   ` def ` ` common_data (list1, list2): ` ` ` ` result ` ` = ` ` False `   ` # move in first list ` ` for ` ` x ` ` in ` ` list1: `   ` # move in the second list ` ` for ` ` y ` ` in ` ` list2: `   ` #if one common ` ` if ` ` x ` ` = ` ` = ` ` y: ` ` result ` ` = ` ` True ` ` return ` ` result `   ` return ` ` result `   ` # driver code ` ` a ` ` = ` ` [` ` 1 ` `, ` ` 2 ` `, ` ` 3 ` `, ` ` 4 ` `, ` ` 5 ` `] ` ` b ` ` = ` ` [` ` 5 ` `, ` ` 6 ` `, ` ` 7 ` `, ` ` 8 ` `, ` ` 9 ` `] ` ` print ` ` (common_data (a, b)) `   ` a ` ` = ` ` [` ` 1 ` `, ` ` 2 ` `, ` ` 3 ` `, ` ` 4 ` `, ` ` 5 ` `] ` ` b ` ` = ` ` [` ` 6 ` `, ` ` 7 ` `, ` ` 8 ` `, ` ` 9 ` `] ` ` print ` ` (common_data (a, b)) `

Exit :

` True Fa lse `

Method 2. Using Set and Property

Using set and property if there is at least one common element, then set (a) & amp; set (b) returns a positive integer, if it does not contain a positive integer then it returns 0. So we insert a into set_a and b into set_b and then check if set_a & amp; set_b for a positive integer or not.

 ` # Python program to check ` ` # if two lists have at least ` ` # one common element ` ` # using a set and property `   ` def ` ` common_member (a , b): ` ` a_set ` ` = ` ` set ` ` (a) ` ` b_set ` ` = ` ` set ` ` ( b) ` ` if ` ` (a_set & amp ; b_set): ` ` return ` ` True `  ` else ` `: ` ` return ` ` False `     ` a ` ` = ` ` [` ` 1 ` `, ` ` 2 ` `, ` ` 3 ` `, ` ` 4 ` `, ` ` 5 ` `] ` ` b ` ` = ` ` [` ` 5 ` `, ` ` 6 ` `, ` ` 7 ` `, ` ` 8 ` `, ` ` 9 ` `] ` ` print ` ` (common_member (a, b)) ` ` `  ` a ` ` = ` ` [` ` 1 ` `, ` ` 2 ` `, ` ` 3 ` `, ` ` 4 ` ` , ` ` 5 ` `] ` ` b ` ` = ` ` [` ` 6 ` `, ` ` 7 ` `, ` ` 8 ` ` , ` ` 9 ` `] ` ` print ` ` (common_member (a, b)) `

Exit:

` True False `

Method 3: using set intersection

Using built-in function set intersections . a_set.intersection (b_set) returns a positive integer if there is at least one common element, otherwise it returns 0. So we insert a in set_a and b in set_b and then check a_set.intersection (b_set) and return depending on the value .

 ` # Python program to check ` ` # if two lists have at least ` ` # one element common ` ` # using intersection set `   ` def ` ` common_member (a, b): ` ` a_set ` ` = ` ` set ` ` (a) ` ` b_set = set (b) `` if len (a_set. intersection (b_set))"  0 : return ( True )  return ( False )    a = [ 1 , 2 , 3 , 4 , 5 ] b = [ 5 , 6 , 7 , 8 , 9 ] print (common_member (a, b))   a = [ 1 , 2 , 3 , 4 , 5 ] b = [ 6 , 7 , 8 , 9 ] print (common_member (a, b)) `

Exit:

` True False `

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