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# All posts tagged algorithms

### The Celebrity problem

Problem statement In a party of people, only one person is known to everyone (celebrity). That celebrity doesn’t know anyone in the party. Find the celebrity if such a person exist. Input Format The first line of the input will contain ( the number of people) and . Each of . . . Read more

### Enumerate primes up to a number N

Problem statement How would enumerate all the prime numbers up to a given range? Solution There way we are going to solve it is using a well-known approach called Sieve of Eratosthenes. The approach is as follows: Assume . 1. First generate a list of integers from 2 to 30. . . . Read more

### Find overlapping appointments

Problem statement Given two unsorted arrays, one with event start times and one with end times, find out if any two events overlap. Solution The key to the solution is to sort the appointments according to their start time in decreasing order, while keeping the correlation between the start and . . . Read more

### Ordinal number to spreadsheet label

Problem statement Write a function that takes the ordinal number of a column in a spreadsheet and returns the label of that column.

Full code

### Find missing duplicate in array

Problem statement Given an array that con­tains dupli­cates of all the num­bers except one num­ber. Find the missing number. Solution We could of course use a HashMap that maps each number to the number of occurrences. This will have a a space complexity of . A better solution is to . . . Read more

### Dortmund Dilemma challenge

Problem statement Borussia Dortmund are a famous football ( soccer ) club from Germany. Apart from their fast-paced style of playing, the thing that makes them unique is the hard to pronounce names of their players ( błaszczykowski , papastathopoulos , großkreutz etc. ). The team’s coach is your friend. . . . Read more

### Missing number in array [0…N]

Problem statement Given an array A = [1, 2, 3, 5, 6, 7 ] and number . This means that the array consists of the numbers from . However, as you see, is missing in . Print the missing number. Solution The solution proposed here makes use of the triangular . . . Read more

### Find duplicate within k indices

Problem statement Given an array of values, design and code an algorithm that returns whether there are two duplicates within indices of each other? Do all, in running time and space. Solution The main idea is to always carry the last -visited elements with each iteration.

### Bogosort challenge

Problem statement Logan is cleaning his apartment. In particular, he must sort his old favorite sequence, , of positive integers in nondecreasing order. He’s tired from a long day, so he invented an easy way (in his opinion) to do this job. His algorithm can be described by the following . . . Read more

### Buy and sell stock once challenge

Problem statement Write a program that takes an array denoting the daily stock price, and returns the maximum profit that could be made by buying and then selling one share of stock. Solution