Python | Find missing numbers in a sorted list range

Last Updated : 11 May, 2020

Given a range of sorted list of integers with some integers missing in between, write a Python program to find all the missing integers.

Examples:

Input : [1, 2, 4, 6, 7, 9, 10]
Output : [3, 5, 8]

Input : [5, 6, 10, 11, 13]
Output : [7, 8, 9, 12]

Method #1 : List comprehension

# Python3 program to Find missing 
# integers in list
          
def find_missing(lst):
    return [x for x in range(lst[0], lst[-1]+1) 
                               if x not in lst]
  
# Driver code
lst = [1, 2, 4, 6, 7, 9, 10]
print(find_missing(lst))

Output:

[3, 5, 8]

Method #2 : List comprehension using zip()

# Python3 program to Find missing 
# integers in list
          
def find_missing(lst):
    return [i for x, y in zip(lst, lst[1:]) 
        for i in range(x + 1, y) if y - x > 1]
  
# Driver code
lst = [1, 2, 4, 6, 7, 9, 10]
print(find_missing(lst))

Output:

[3, 5, 8]

Method #3 : Using set

The use of Python set is an efficient and tricky way to find the missing numbers in the list. We convert the list to set and simply output the difference between this set and a set that contains integers ranging from min(lst) and max(lst).

# Python3 program to Find missing 
# integers in list
          
def find_missing(lst):
    return sorted(set(range(lst[0], lst[-1])) - set(lst))
  
# Driver code
lst = [1, 2, 4, 6, 7, 9, 10]
print(find_missing(lst))

Output:

[3, 5, 8]

Method #4 : Using difference()

This is a similar approach to the previous one with a slight difference that instead of using ‘-‘ operator to find the difference between both the sets, we can use Python difference() method.

# Python3 program to Find missing 
# integers in list
          
def find_missing(lst):
    start = lst[0]
    end = lst[-1]
    return sorted(set(range(start, end + 1)).difference(lst))
  
# Driver code
lst = [1, 2, 4, 6, 7, 9, 10]
print(find_missing(lst))

Output:

[3, 5, 8]

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