Python – Create nested list containing values as the count of list items
Last Updated :
06 Feb, 2023
Given a list, the task is to write a Python program to create a nested list where the values are the count of list items.
Examples:
Input: [1, 2, 3]
Output: [[1], [2, 2], [3, 3, 3]]
Input: [4, 5]
Output: [[1, 1, 1, 1], [2, 2, 2, 2, 2]]
Method 1: Using nested list comprehension
The list will contain the count of the list items for each element e in the list we will create a list in the list with size e, in each list we will append the element e for e times.
Python3
l = [1, 2, 3, 4, 5]
l = [[i+1 for j in range(l[i])] for i in range(len(l))]
print(l)
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Output:
[[1], [2, 2], [3, 3, 3], [4, 4, 4, 4], [5, 5, 5, 5, 5]]
Time Complexity : O(N^2)
Space Complexity : O(N^2)
Method 2:
The list will contain the count of the list items iterate the for loop for L times i.e. length of the list. Now at each element append a list, The appended list will be of the size count.
Python3
l = [1, 2, 3, 4, 5]
for i in range(len(l)):
l[i] = [i+1 for j in range(i+1)]
print(l)
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Output:
[[1], [2, 2], [3, 3, 3], [4, 4, 4, 4], [5, 5, 5, 5, 5]]
Time Complexity : O(N^2)
Space Complexity : O(N)
Method 3: Using *
Python3
l = [1, 2, 3, 4, 5]
nl=[]
for i in range(0,len(l)):
j=[i+1]
nl.append(j*l[i])
print(nl)
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Output
[[1], [2, 2], [3, 3, 3], [4, 4, 4, 4], [5, 5, 5, 5, 5]]
Time Complexity : O(N^2)
Space Complexity : O(N)
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