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NPTEL Joy Of Computing Using Python Week 12 Programming Assignment 2025

In this the following topics are discussed which are most important to the exam:

• Page Ranking
• Graphs
• Nodes
• Collatz Conjecture

Last Date: 17-04-2025

Q1. Given a sorted list nums in non-decreasing order, where every element appears twice except for one unique element, find and return the single number.

Example 1:

Input

nums = [1, 1, 2, 2, 3, 3, 4, 5, 5, 6, 6]

Output

4

Example 2 :

Input 

nums = [1, 1, 3, 5, 5]

Output

3

Constraints:

n==len(nums)

1<=n<=104

Program Code:

def singleNonDuplicate(nums):

    result = 0

    for num in nums:

        result ^= num

    return result {codeBox}

Q2. You are given a string s consisting of only lowercase English letters. Your task is to return a list of unique characters from the string, sorted in descending order based on their frequency of occurrence.

• If two or more characters have the same frequency, they should be sorted in alphabetical order.

Input:

• A string s
• The string consists of only lowercase English characters ('a' to 'z').

Output:

• A list of unique characters sorted by frequency (highest to lowest).
• If characters have the same frequency, they should appear in alphabetical order.

Example 1:

Input: s = "tree"

Output: ['e', 'r', 't']

Example 2 :

Input: s = "bbccddaaa"

Output: ['a', 'b', 'c', 'd']

Explanation:

The frequency of each character:

• 'a' → 3
• 'b' → 2
• 'c' → 2
• 'd' → 2

Since 'b', 'c', and 'd' have the same frequency, they are sorted alphabetically.

Program Code:

from collections import Counter

def frequencySort(s):

    freq = Counter(s)  

    return sorted(freq, key=lambda x: (-freq[x], x))  {codeBox}

Q3. Write a Python function subsequence(l1,l2) that takes two sorted lists as arguments and returns True if the the first list is a subsequence of the second list, and returns False otherwise.

A subsequence of a list is obtained by dropping some values. Thus, [2,3,4] and [2,2,5] are subsequences of [2,2,3,4,5], but [2,4,4] and [2,4,3] are not.

For Example : 

Input: subsequence([2,2,5],[2,2,3,4,5])

Output: True 

Program Code:

def subsequence(l1, l2):

    i, j = 0, 0  

    

    while i < len(l1) and j < len(l2):

        if l1[i] == l2[j]:  

            i += 1

        j += 1  

    

    return i == len(l1)  {codeBox}

Conclusion

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