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Strings in Python are immutable, meaning you cannot modify individual characters directly. When you need to change a character at a specific index, you must create a new string using slicing and concatenation. For example, if we have s = "python", i = 3, and c = 'P', attempting s[i] = c will raise a TypeError: 'str' object does not support item assignment. Algorithm To replace a character at index i with character c ? Extract the left part: s[0:i] Extract the right part: s[i+1:] Concatenate: left + c + right Using String ... Read More
Sometimes we need to split a string into individual words and then join them back together with commas instead of spaces. Python provides simple built-in methods to accomplish this task efficiently. So, if the input is like s = "Programming Python Language Easy Funny", then the output will be Programming, Python, Language, Easy, Funny Algorithm To solve this, we will follow these steps − words − Create a list of words by applying split() function on the string with delimiter " " (space) result − Join each ... Read More
The hash() function in Python computes a hash value for hashable objects like tuples. Hash values are integers used internally by Python for dictionary keys and set membership tests. Tuples are hashable because they are immutable, unlike lists which cannot be hashed due to their mutable nature. Syntax hash(object) Where object must be a hashable type (int, float, string, tuple, etc.). Example Let's find the hash value of a tuple containing integers − def solve(t): return hash(t) t = (2, 4, 5, 6, 7, 8) result ... Read More
When working with lists in Python, you often need to sort or reverse them without modifying the original list. Python provides sorted() and reversed() functions that return new objects, unlike sort() and reverse() which modify the list in-place. Problem Statement Given a list of numbers, create a reversed version and a sorted version without changing the original list. Example Input and Output If the input is l = [2, 5, 8, 6, 3, 4, 7, 9], the output should be ? Reversed: [9, 7, 4, 3, 6, 8, 5, 2] Sorted: [2, 3, 4, ... Read More
When working with student scores stored in a dictionary, calculating the average score for each student is a common task. In Python, we can achieve this by iterating through the dictionary and computing the mean of each student's scores. So, if the input is like scores = {'Amal' : [25, 36, 47, 45], 'Bimal' : [85, 74, 69, 47], 'Tarun' : [65, 35, 87, 14], 'Akash' : [74, 12, 36, 75]}, then the output will be [38.25, 68.75, 50.25, 49.25] where 38.25 is average score for Amal, 68.75 is average score for Bimal and so on. Algorithm ... Read More
Given an array A of size n and two values p and q, we need to find the expected sum of subarrays after performing specific operations. This problem involves probability calculations and matrix operations to determine the expected value. Problem Understanding We can perform two types of operations on array A: Randomly select two indices (l, r) where l < r, then swap A[l] and A[r] Randomly select two indices (l, r) where l < r, then reverse subarray A[l..r] After performing the first operation p times and second operation q times, we randomly ... Read More
Suppose we have the names and grades for each student in a nested list, we have to display the names of any students having the second lowest grade. If there are more than one students with the second lowest grade, reorder these in alphabetical order and print each name on a new line. So, if the input is like students = [['Amal', 37], ['Bimal', 37], ['Tarun', 36], ['Akash', 41], ['Himadri', 39]], then the output will be Amal and Bimal, both having the second lowest score of 37, displayed in alphabetical order. Algorithm Steps To solve this, we ... Read More
Finding the runner-up score means identifying the second highest score in a list of participants. This is a common problem in competitive programming and data analysis. So, if the input is like scores = [5, 8, 2, 6, 8, 5, 8, 7], then the output will be 7 because the winner score is 8 and second largest score is 7. Algorithm To solve this, we will follow these steps − Initialize winner := -99999 Initialize runner_up := -99999 For each score in the ... Read More
A palindromic border is a substring that appears as both a prefix and suffix of a string, and the substring itself is a palindrome. For example, in the string 'ababab', the substring 'ab' is a border, but not palindromic. However, in 'pqpqp', the substring 'p' is both a border and palindromic. Given a string, we need to find the sum of palindromic borders across all possible substrings. The result should be returned modulo 10^9 + 7. Example For the string 'pqpqp', there are 15 total substrings, but only 4 have palindromic borders ? pqp : ... Read More
When analyzing M expressions with results ranging from 1 to N, we need to find the expected value of the maximum frequency among all possible outcomes. This problem involves calculating probabilities using combinatorics and the inclusion-exclusion principle. Problem Understanding Given M expressions with results in range [1, N], we want to find the expected value of the maximum frequency. For each possible sequence of expression results, we count the frequency of the most common value. For example, with M = 3, N = 3: Sequence Maximum Frequency 1113 1122 1132 1212 1222 1231 ... Read More