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Questions tagged [greedy-algorithms]

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Questions about algorithms that make at each step the locally optimal choice.

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Best approach to resource allocation problem

Problem The enemy army has taken $n$ of our cities. In each city $i$ the enemy has placed $e_i$ soldiers. We have $n$ teams, each team $j$ with $d_j$ soldiers. If we place more soldiers in a city ...
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1answer
20 views

Algorithm of split graph $G=(V,E)$ to 2 groups that at least half of the edges are between the groups [duplicate]

Can someone remind me the algorithm that split vertex of graph to 2 groups that at least half of the edges are external, I mean between the groups. As I remember it was a greedy algorithm, each time ...
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1answer
49 views

What Makes an Algorthim Greedy [Graph Coloring Algorithm]

I have a simple graph G = (V,E) and each vertex has a range [a,b].Every two vertices are connected only if [a_1,b_1] and [a_2,b_2] have a common subrange. Each range of vertex is rV1 = [0,5] rV2 = [1,...
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1answer
37 views

Is the following Greedy algorithm to generate Gray Codes always correct?

I recently solved the basic problem of generating a n-bit Gray Code. The solution I used involved building larger-bit Gray Codes from smaller ones recursively (the solution I've seen on most websites)....
2
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2answers
79 views

Maximize number of subsets

Given a list of subsets $S_1, \ldots, S_n$ of the universal set $U = \{e_1,\ldots, e_m\}$, find a subset $S \subset U$ of size $k$ that contains the maximum number of subsets $S_i$. In another words, $...
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1answer
20 views

How to (Efficiently) Sort a List of Items with Parent/Child Relationship

I have a list of items that have a parent/child/grandchild/etc. type of relationship. Each item has a list of descendants, and an _.isDescendentOf(other) member ...
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1answer
38 views

Maximum Independent Set of special Directed Graph

I was given this special type of Directed Graph and was asked to find it's Maximum Independent Set. Graph Properties : Graph has $N$ vertices and $N$ edges There can be no edge from a vertex $v$ to ...
3
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1answer
62 views

Greedy algorithm for subset sum on powers of 2

I have some $n$ numbers which are powers of $2$, say $a_1,a_2,a_3,\ldots,a_n$ which are not necessarily all distinct. I have option to give them any sign. I have to find if I can make their sum after ...
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0answers
16 views

Rearrange string k distance Apart

The question statement is as follows: Given a non-empty string s and an integer k, rearrange the string such that the same characters are at least distance k from each other. All input strings are ...
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0answers
16 views

Greedy Best-First Search Performance for Tree and Graph Space

I am currently reviewing the GBFS algorithm and when looking at its completeness I am confused between the difference of it being not optimal in Tree Search for Finite and Infinite Spaces that it is ...
3
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0answers
18 views

Spanning hypertree which connects the vertices as slowly as possible

I want to find a reference for the following problem or a similar problem for my paper. I found a greedy algorithm for this problem, but writing such an algorithm in a paper is not common in my area, ...
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2answers
45 views

Highest Product of X Items

šŸ§© How do you find the highest product of X items? This should optimize for runtime complexity and protect from overflows from large products. Inputs An array of both positive and negative Ints ...
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1answer
59 views

Greedy algorithm for problem asking for solution of size *at most* $k$

Given an integer $k$ and a complete weighted bipartite graph with sides $A,B$ in which the weight of the edge $(i,j)$ is $c_{ij} \geq 0$, we want to find a set $S$ of at most $k$ edges that maximizes $...
2
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1answer
38 views

2-Approximation algorithm for for messages across a cyclic network

Question There are $n$ computers arranged in a cycle ($1,2,3..,n,1$), with undirected edges between adjacent computers. There are $m$ messages that need to be delivered. Message $i$ ($1 \le i \le m$) ...
2
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1answer
31 views

Modified topological sort

I recently asked a related question at the theoretical CS stack exchange, but I have modification to the problem that I think is a bit tougher. This seems like a better place anyways. Let's define a &...
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0answers
29 views

Does the existence of a matroid structure imply that the greedy algorithm is optimal?

I was going through the topic of matroid structures for the problems like Activity selection ,minimum spanning tree. I also came to know how to solve if a problem exhibits matroid structure. The ...
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0answers
25 views

Greedy Proof: For coin denomination systems, faster proof to ensure greedy solution yields the optimal solution

I have reasons to believe that there is a faster way to confirm, that for coin denomination systems if the greedy solution yields the optimal solution or not. I believe that if you check that for all ...
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1answer
105 views

How to understand the solution to Task Scheduler problem on LeetCode?

LeetCode Task Scheduler problem is the following: Given a characters array tasks, representing the tasks a CPU needs to do, where each letter represents a different task. Tasks could be done in any ...
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1answer
43 views

Serving $k$ customers with bounded time window

A person provides a service and he/she can serve $k$ clients each minute. Now, client number $i$ comes at the beginning of minute $a_{i}$ and waits $w_{i}$ minutes to receive the service and if they ...
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1answer
41 views

Ordering the tasks to minimize penalties

So I just started learning greedy algorithms and I have a problem that I want to solve. The statement is as follows: In your calendar you have an $L$ list of all the tasks you need to complete today. ...
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1answer
84 views

Correctness proof of a greedy approximation algorithm

How do I prove the correctness of this algorithm?
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0answers
28 views

Maximize the minimum gap while scheduling within intervals?

Problem There are N intervals in which a particular integer can be chosen. What is the maximum possible minimum gap between each integer if one integer is chosen for each of those intervals? For ...
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2answers
59 views

Why this problem has such a simple solution? How would you avoid looking for more complex solutions first?

There's a problem whose solution startles me because at first sigh, I wouldn't imagine that it could be solved so easily. The problem is: There are n tasks, each task ...
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1answer
34 views

Mathematical expression for the quantity that we are maximising in the stock buying and selling problem

Problem Statement: Say you have an array prices for which the $i^{th}$ element is the price of a given stock on day $i$. Design an algorithm to find the maximum profit. You may complete as many ...
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2answers
59 views

What is an algorithm for minimizing the standard deviation of m sums summed from n summands? [with attempt]

I have m bins (sums) and n summands. Each summand goes into a bin. In order to minimize the standard deviation, I have a greedy algorithm that appears to accomplish this. I am not sure of the name, ...
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1answer
34 views

Prove following statement about Kruskal Algorithm

Let G be undirected graph, G=(V,E), and all edge weights are distinct. Consider an edge e=(u,v)āˆˆE that wasn't included in the solution obtained from applying Kruskal Algorithm to G. Prove that this ...
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0answers
49 views

Find the maximum number of valid cartesian coordinates

Given a list X containing m number of x coordinates and a list Y containing m number of y coordinates. The coordinate (x, y) is valid if and only if the difference between x and y is less than or ...
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0answers
39 views

Choosing a method for algorithmic problems - is it an art or science?

I've been doing lot of programming challenges lately (such as on leetcode.com) and often find myself in a situation when I cannot pick a method for solving a problem. I stuck with questions like - ...
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18 views

Minimizing the length a Boolean Algebra Expression in disjunctive normal form

I'm looking to minimize the length of an expression in boolean algebra that has been given in disjunctive normal form and is free from redundancy. To remove redundancy from the original expression I ...
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1answer
81 views

Binary string satisfying several constraints

I'm trying to solve this problem, but without success. Problem: You're given a binary string where some of the bits are replaced by ?. You're also given several ...
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0answers
45 views

Algorithm for summation with lowest maximum temporary sum

I've got this problem on my last exam, which I struggle to deal with. Let's say we have array of $N$ integers (it can be float too, but let's say integers for sake of simplicity. We need to sum those ...
4
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2answers
226 views

Difficulty in understanding the proof of the lemma : “Matroids exhibit the optimal-substructure property”

I was going through the text "Introduction to Algorithms" by Cormen et. al. where I came across a lemma in which I could not understand a vital step in the proof. Before going into the lemma ...
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1answer
400 views

Greedy sequential/parallel task scheduling

We have N tasks that need to be scheduled for processing. Each task consists of two parts that need to executed in order. The first one is guarded by a mutex and ...
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1answer
21 views

An independent d-division

I would love to have a direction for the following exercise (the material for this exercise is greedy algorithms): Let $G = (V,E)$ an undirected graph whose vertices $V = \{v_1,\dots,v_n\}$ appear in ...
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1answer
70 views

Negative cycle detection using Bellman-Ford and its correctness

I recently started studying algorithms on my own using Cormen and MIT algo videos in YouTube. I am going thru Bellman-Ford. I have 2 doubts about the correctness of the algorithm: Why are we ...
3
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1answer
123 views

Using a greedy algorithm to find a cut S which at least half of the edges cut

Let $G$ be an undirected graph. Find a greedy algorithm that finds a cut $S$ which at least half of the edges cut. I tried to think about something like choosing the vertex with the highest degree, ...
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0answers
35 views

Scheduling algorithm for overlapping jobs - single resource?

I have a single resource that will need to shared for running multiple parallel jobs. Think of the resource as a straight line numbered from 1 to 100. The jobs occupy part of the line while they are ...
0
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1answer
57 views

Three City Scheduling

I came across the following interview question There are 2N people a company is planning to interview. The cost of flying the i-th person to city A is costs[i][0], and the cost of flying the i-...
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0answers
28 views

Remove vertices to get k-connected components

In a graph, I need to remove some vertices in order to get at least k-connected components. The no. of removed vertices should be low. Is there a heuristic that I could follow for this?
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20 views

Set Cover: Understanding the algorithm with an example

I am trying to follow the following link: Solution for an example They have provided solution for an example using the greedy algorithm. I have got following questions: (1)Why start with Z, cost is 7, ...
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0answers
32 views

Does this problem have a formal name?

I have come across the following problem but am unable to understand the solution for it. Hence I would like to know if it has a formal name then, I can search for it and read about it in more detail. ...
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1answer
50 views

Problem related to set partitioning

Let $A_j=\{(a^i_j,b^i_j)~:~ 0 \leq i \leq n,\text{and } a^i_j,b^i_j \in \mathbb{Z}^+\}$ Given sets $A_1,\ldots, A_{p}$ and a positive integer $k$, the problem is to check whether there exists one ...
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1answer
142 views

Minimum steps to sort array [closed]

Consider you have a permutation of $1$ to $n$ in an array $array$. Now select three distinct indices $i$,$j$,$k$, there is no need to be sorted. Let $array_i$, $array_j$ and $array_k$ be the values ...
2
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1answer
77 views

Proof of a greedy algorithm used for a variation of bin-packing problem

We are given an array of weights $W$ (all weights are positive integers), and we need to put the weights inside bins. Each bin can hold a maximum of Max_val, and each weight is at most Max_val. The ...
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1answer
16 views

How proof of Hoffman algorithm greedy property starts with optimal tree T?

In this paper Claim 1 states that x and y are smallest probability and there is optimal code tree in which this two characters are siblings at the maximum depth. In proof to that claim, author starts ...
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0answers
87 views

Greedy algorithm to divide objects into the lowest number of groups of a maximum size

I have n objects of independent size s, and need to group them so that the sum of the sizes of each group is smaller than a given maximum size, and the number of groups is the smallest possible. I ...
2
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1answer
214 views

N numbers, N/2 pairs. Minimizing the maximum sum of a pairing. Proving greedy algorithm

So say I have n numbers, where n is even. I want to pair the numbers such that the maximum sum of the pairs is minimized. For example -2, 3, 4, 5. The ideal pairing is (-2, 5), (3, 4), since its ...
2
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1answer
60 views

Proof for an algorithm to minimize $\max(a, b, c) - \min(a, b, c), a \in A, b \in B, c\in C$, A, B, C are arrays in ascending order

Problem Statement I came across this problem here. For given arrays $A$, $B$ and $C$ arranged in ascending order, we need to minimize the objective function $f(a, b, c) = \max(a, b, c) - \min(a, b, c)...
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0answers
47 views

Looking for an algorithm or similar mathematical problem for trading ownerships in shared property

Suppose there is $N$ property. Each property is owned by multiple person. (they have shared ownership) For example: $Person_1$ owns 22% of $Property_1$, $Person_2$ owns 35% of $Property_1$ and $...
2
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1answer
437 views

Gas Station Problem - Dijkstra's Algorithm variation

I am trying to find an algorithm which finds the least expensive route from one town to another. This is the general setup. There are a series of one-way roads from some towns to other towns. Not ...

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