I checked from website, this is called unimodal permutation, which defines as a sequence that has only one local maximum. For example n = 5:

```
12345
12354
12453
12543
13452
13542
14532
15432
23451
23541
24531
25431
34521
35421
45321
54321
```

Is there an algorithm to get the kth unimodal permutations?

Answer:

The trick here is to index the sequence in binary

```
1234
----
12345 (0000)
12354 (0001)
12453 (0010)
12543 (0011)
13452 (0100)
13542 (0101)
14532 (0110)
15432 (0111)
23451 (1000)
23541 (1001)
24531 (1010)
25431 (1011)
34521 (1100)
35421 (1101)
45321 (1110)
54321 (1111)
```

and then observe that the numbers 1..4 appear before the 5 if and only if their bit is 0. In Python:

```
def kth_unimodal(n, k): # k is 0-indexed
left = []
right = []
for j in range(1, n): # 1..n-1
if k & (1 << (n - 1 - j)):
right.append(j)
else:
left.append(j)
left.append(n)
left.extend(reversed(right))
return left
```

string,algorithm,palindrome

Given length L find the shortest string >= L formed only of as & bs such that adding some character (Either a or b) doesn't produce a new palindrome substring (never seen before palindrome) For example for L = 1 there is the string aabbaba, adding "a" to it to...

python,algorithm,time-complexity,longest-substring

Someone asked me a question Find the longest alphabetically increasing or equal string composed of those letters. Note that you are allowed to drop unused characters. So ghaaawxyzijbbbklccc returns aaabbbccc. Is an O(n) solution possible? and I implemented it code [in python] s = 'ghaaawxyzijbbbklccc' lst = [[] for i...

ruby,algorithm,search,recursion

I'm working through a toy problem in Ruby: how to produce all possible 10-digit phone numbers where each successive number is adjacent to the last on the keypad. I've represented the adjacent relationships between numbers, and have a recursive function, but my method isn't iterating through the whole solution space....

python,regex,algorithm,python-2.7,datetime

If I knew the format in which a string represents date-time information, then I can easily use datetime.datetime.strptime(s, fmt). However, without knowing the format of the string beforehand, would it be possible to determine whether a given string contains something that could be parsed as a datetime object with the...

c++,algorithm

I'm trying to make a program to check whether the word "nadia" is present with this sequence in a string. if you can delete zero or more characters to get this word then you should print "YES" else print "NO". Can anyone help me find what are the test cases...

c++,algorithm

Having a hard time designing an efficient algorithm that accomplishes the following. If I start with a 2d vector A, A = [1 2 3; 2 3 4; 5 6] I want to take the rows that contain common elements and combine them (removing duplicates) resulting in 2d vector B:...

algorithm,bit-manipulation

Given a 64 bit number, I need to extract every other bit from it, and convert it into a number: decimal: 357 binary: 0000 0001 0110 0101 odd bits: 0 0 0 1 1 0 1 1 decimal: 27 Any idea of a good algorithmic way to do it? And...

algorithm,coordinates,coordinate-systems,coordinate

I'm writing a program for visualizing crystals. As a part of the program, I have to generate all different basic points in a lattice structure. For those that aren't familiar with crystallography, you can find the most general cases of these structures here: https://en.wikipedia.org/wiki/Hermann%E2%80%93Mauguin_notation#Lattice_types The problem was that I wanted...

c,algorithm

I try find out what is wrong with the program that takes n - size of serials and this same number of elements numbers. With n = 4 and numbers 1, 2, 3, 4 I get output: 1, 0, 2293428, 1990567906. Somewhere in the code something is not okey, but...

c++,algorithm,parallel-processing,c++14

Proposal N3554 (A Parallel Algorithms Library) for C++14, proposes (among other things), what seem to be parallel versions of the current std::partial_sum, e.g.: template< class ExecutionPolicy, class InputIterator, class OutputIterator, class BinaryOperation> OutputIterator inclusive_scan( ExecutionPolicy &&exec, InputIterator first, InputIterator last, OutputIterator result, BinaryOperation binary_op); With the explanation Effects: For each...

algorithm,recursion,permutation

Assuming I have a list of elements [1,2,3,4,] and a number of bins (let's assume 2 bins), I want to come up with a list of all combinations of splitting up items 1-4 into the 2 bins. Solution should look something like this [{{1}, {2,3,4}}, {{2}, {1,3,4}}, {{3}, {1,2,4}}, {{4},...

algorithm,math,statistics,variance,standard-deviation

I'm successfully using Welford's method to compute running variance and standard deviation as described many times on Stack Overflow and John D Cook's excellent blog post. However in the stream of samples, sometimes I encounter a "rollback", or "remove sample" order, meaning that a previous sample is no longer valid...

algorithm,discrete-mathematics

I'm doing an online course and i'm stuck on this question. I know there are similar questions but they don't help me. What is the order of growth of the worst case running time of the following code fragment as a function of N? int sum = 0; for (int...

javascript,algorithm,recursion

While working through some Coderbyte challenges, I was able to solve the following problem recursively, but was hoping to get some feedback on how I can improve it. Have the function AdditivePersistence(num) take the num parameter being passed which will always be a positive integer and return its additive persistence...

python,algorithm,sorting,math

I am looking for a basic algorithm that gives more weigh to the recent reviews. So, the output value of the algorithm is mutable. For example, two reviews with exactly the same score, will have a different ranking based on the timestamp of the creation. Review_1 Score 10 creation 10/5/2014...

algorithm,numerical-methods,numerical,numerical-integration

Consider the following differential equation f(x) = g'(x) I have a build a code that spits out values of the function f(x) for the variable x, where x goes from 0 to very large. Now, I'm looking for a scheme that will analyse these values of f(x) in order to...

c,string,algorithm,data-structures

int myStrCmp (const char *s1, const char *s2) { const unsigned char *p1 = (const unsigned char *)s1; const unsigned char *p2 = (const unsigned char *)s2; while (*p1 != '\0') { if (*p2 == '\0') return 1; if (*p2 > *p1) return -1; if (*p1 > *p2) return 1;...

c,algorithm,security,math,encryption

I'm trying to reverse the following code in order to provide a function which takes the buffer and decrypts it. void crypt_buffer(unsigned char *buffer, size_t size, char *key) { size_t i; int j; j = 0; for(i = 0; i < size; i++) { if(j >= KEY_SIZE) j = 0;...

c#,regex,algorithm

I'm making a script to try and hack into an account whose login password is at least 8 characters long and includes at least 1 number, 1 special character and 1 capital letter. I will use brute force. Is there a compact, elegant and efficient way to iterate through every...

python,algorithm,permutation

I'm trying to write a function that would input a list (of pre-determined length) and output the permutation of that list according to my choice of re-ordering. For example, suppose I have the list [1,'a',12,'b','poppy'] and I have the permutation (3,4,5,2,1) Then the function output would be a list with...

c++,algorithm,inheritance,time-complexity

Here I have 800 derived classes of Base and a list of 8000000 objects of these types, which can be of any order. The goal is to separate the list into the 800 types as efficiently as possible. Here I have written two functions to do that. The first is...

algorithm,dynamic-programming,knapsack-problem

I am familiar with the 0-1 knapsack problem and when you are given a certain number of copies from each item but I can figure out how to solve it when you are given infinite copies of each item using dynamic programming. I am trying to solve it by hand...

algorithm

You are managing a software project that involves building a computer-assisted instrument for medical surgery. The exact placement of the surgical knife is dependent on a number of different parameters, usually at least 25, sometimes more. Your programmer has developed two algorithms for positioning the cutting tool, and is seeking...

c++,algorithm,math,recursion

I'm trying to find all possible solutions to the 3X3 magic square. There should be exactly 8 solutions. My code gets them all but there are a lot of repeats. I'm having a hard time tracking the recursive steps to see why I'm getting all the repeats. // This program...

function,operators,xquery,sequence,aggregation

I'm trying to execute a XQuery sum function in a multiplication of two XML elements, but it has been difficult to avoid the iteration in a sequence of elements. For example, consider this case: sample data: <Orders> <Order> <OrderKey>1</OrderKey> <LineItem> <LineNumber>1</LineNumber> <Quantity>41</Quantity> <ExtendedPrice>70848.0000</ExtendedPrice> <Discount>0.0913</Discount> <Tax>0.0663</Tax> <ReturnFlag>A</ReturnFlag>...

c#,arrays,algorithm,random,cycle

The following LINQPad code generates random sequence of unique integers from 0 to N and calculates the length of cycle for every integer starting from 0. In order to calculate cycle length for a given integer, it reads value from boxes array at the index equal to that integer, than...

python,algorithm

I am trying to calculate least completion time of a project schedule, which has n number of tasks and each task can have a dependency task. example Task ID Duration Days Dependent ID 1 10 0 2 3 0 3 6 1 4 5 2 5 10 1 Task with...

c++,algorithm,matrix

I am trying to print the right hemisphere of a matrix. If we draw the main and the secondary diagonals in a matrix we see that we got 4 equal parts, the right part is called (in my algorithms textbook) the right hemisphere of a square matrix. For example, in...

javascript,algorithm

I accidentally got undefined == true and undefined == false that both of them returns false. But !undefined returns true. And this is the question: What's the algorithmic difference(s) between !someVariable and someVariable == false? If i want to explain it more, type undefined == false ? 't' : 'f'...

php,algorithm,digits

I'm following the programming test, and there are questions like this From this consecutive digits: 123456789101112131415161718192021.... For example The 10th digit is 1 The 11th digit is 0 and so on What is the 1,000,000th digit? What is the 1,000,000,000th digit? What is the 1,000,000,000,000th digit? Your solution should run...

c#,sequence,formula

I have a semaphore variable with 5 states. I can increase the state using this cicle X = (X + 1) % 5 For X = {0, 1, 2, 3, 4} generate {1, 2, 3, 4, 0}. But if I try go in the other direction decreasing the state, doesn't...

c++,arrays,algorithm,sum

I tried to find all pairs in the array with sum equal to k, the solution to that takes O(n*log(n)) time. Here is the code snippet - map<int,int> mymap; map<int,int>::iterator it; cin>>n>>k; for( int i = 0 ; i < n ; i++ ){ cin>>a; if( mymap.find(a) != mymap.end() )...

java,algorithm,function,genetic-programming,convergence

I have a few questions about my genetic algorithm and GAs overall. I have created a GA that when given points to a curve it tries to figure out what function produced this curve. An example is the following Points {{-2, 4},{-1, 1},{0, 0},{1, 1},{2, 4}} Function x^2 Sometimes I...

algorithm,big-o

I was doing some reading on logarithms and the rate of growth of the running time of algorithms. I have, however, a problem understanding the Big-Ω (Big-Omega) notation. I know that we use it for 'asymptotic lower bounds', and that we can express the idea that an algorithm takes at...

algorithm

I attended a programming competition(it has ended now). I don't know why my solution is giving WA, I read the editorial, saw other people solution but unable to find a flaw in my solution. Obviously I am missing somewhere. Please help! Question Link My Solution My approach If the pattern...

c++,arrays,algorithm,recursion

I'm trying to write a recursive algorithm that returns true if at least one array[i] == i. And false if there is no array[i] = i. Also, the parameters needed are (int * arr, int start, int end). So i'll be traversing the array with a pointer. For example: int...

algorithm,data-structures

In an exam I see a question: Which one of the following is true? For a binary search, the best-case occurs when the target item is in the beginning of the search list. For a binary search, the best-case occurs when the target is at the end of the search...

algorithm,graph,tree,runtime,big-o

I have a possible solution for the following question, but not sure if correct: Assume we have already found a minimum spanning tree T for a weighted, undirected graph G = (V,E). We would like to be able to efficiently update T should G be altered slightly. An edge is...

c++,algorithm,graph

Someone can help me to think in the better way to adapt Dijkstra's Algorithm in these conditions? All I thought didn't was good. Example of input: GP4578 MADRID 01:00 PORTO 02:00 IK6587 PORTO 03:00 VALENCIA 05:00 05:30 TENERIFE 08:00 AB5874 VALENCIA 05:40 BERLIM 10:00 "VALENCIA 05:00 05:30" This is a...

algorithm,optimization,dynamic-programming,frequency

I have the following problem and I only have a slight idea about it: Consider a tape storage problem. Given n files of length l1,...,ln and frequencies with which they are accessed f1,...,fn, where sum of all frequencies is 1 and 0<fi<1. "Optimal" means to minimize the average retrieval time...

algorithm,graph,cycle,dfs

I came around one of those questions in my exams: Topologocial sorting using Kahn's Algorithm requires the graph to be DAG (Directed Acyclic Graph). How can we determine if a graph contains no cycles without using DFS/BFS first? I am trying to answer that for too long now and I...

algorithm,set,combinatorics,backtracking

For a set of the form A = {1, 2, 3, ..., n}. It is called partition of the set A, a set of k<=n elements which respect the following theorems: a) the union of all the partitions of A is A b) the intersection of 2 partitions of A...

algorithm,scala,priority-queue

I've defined a priority queue like so import scala.collection.mutable.PriorityQueue ... val queue = new PriorityQueue[(Int,Int)]() I want to use this ordering: If we are comparing two items A and B in the queue, A is bigger than B if the first element of its (Int,Int) tuple is larger than B's....

c++,algorithm

The project Euler problem 5 is stated as : "2520 is the smallest number that can be divided by each of the numbers from 1 to 10 without any remainder. What is the smallest positive number that is evenly divisible by all of the numbers from 1 to 20?" Here's...

algorithm,go

I am trying to solve the following problem from project euler (please take a look at description and the example in the link, but here is the short explanation). in the matrix, find the minimal path sum from the top left to the bottom right, by moving left, right, up,...

algorithm,graph,tree,runtime,big-o

I am having trouble with the following question: Assume we have already found a minimum spanning tree T for a weighted, undirected graph G = (V,E). We would like to be able to efficiently update T should G be altered slightly. An edge is removed from G to produce a...

java,c++,algorithm,recursion,dfs

For example, given a set like below - S=[1,3] we want to get the list of list with following values: [[],[1],[3],[1,3]] I used C++ with the following code and it worked perfect for me. However, after I changed it to Java, the code didn't give me right results. Any help?...

c++,algorithm,sorting,c++11

I have implemented three different sorting algorithms and now I want to confirm that my approach of counting the total number of comparisons is correct. In my mind, the number of comparisons shouldn't be tied to the conditional branches because if the condition isn't met, the comparison was still made...

php,algorithm,assign,subgraph,pairing-heap

In the following we are facing the problem of multiple assignments of the hungarian algorithm. Scenario: We have 100 students and 5 courses, which the students can vote with priority. So every student will get assigned for one specific cours. Priority from 1 to 5. 1 lowest 5 highest The...

algorithm,graph

I am looking for an algorithm that finds minimal subset of vertices such that by removing this subset (and edges connecting these vertices) from graph all other vertices become unconnected (i.e. the graph won't have any edges). Is there such algorithm? If not: Could you recommend some kind of heuristics...