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

  • Last Updated : 21 Nov, 2018

Given two lists a, b. Check if two lists have at least one element common in them.

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 : Traversal of List

Using traversal in two lists, we can check if there exists one common element at least in them. While traversing two lists if we find one element to be common in them, then we return true. After complete traversal and checking, if no elements are same, then we return false.






# Python program to check 
# if two lists have at-least 
# one element common
# using traversal of list
  
def common_data(list1, list2):
    result = False
  
    # traverse in the 1st list
    for x in list1:
  
        # traverse in the 2nd 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))

Output:

True 
False

Method 2 : Using Set and Property

Using set’s and property, if there exists at least one common element then set(a)&set(b) returns a positive integer, if it does not contains any positive integer, then it returns 0. So we insert a in set_a and b in set_b and then check if set_a & set_b for a positive integer or not.




# Python program to check 
# if two lists have at-least 
# one element common
# using set and property
  
def common_member(a, b):
    a_set = set(a)
    b_set = set(b)
    if (a_set & 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))

Output:

True 
False

Method 3 : Using Set Intersection

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




# Python program to check 
# if two lists have at-least 
# one element common
# using set intersection
  
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))

Output:

True 
False

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