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Alice wants to throw a party and is deciding whom to call. She has n people to choose from, and she has made up a list of which pairs of these people know each other. She wants to pick as many people as possible, subject to two constraints: at the party, each person should have at least five other people whom they know and five other people whom they don’t know. Give an efficient algorithm that takes as input the list of n people and the list of pairs who know each other and outputs the best choice of party invitees. Give the running time in terms of n

Short Answer

Expert verified

Each vertex with each member inside the vertex set, such asuandv , indicates that the person v knows the person u . So, find the subset v where another vertex has a value greater than 5 , then repeat the process with both the modified degrees for every node until a network is formed in which neither vertex may be destroyed after the procedure is finished. As a result, the running time's total complexity has increased.

Step by step solution

01

Individual String ‘Fi’

Assuming that each individual attends the party with at least 5 different other things they trust and five others they don't. Throughout a few places in the question, every string 'fi' has been substituted with '?'. If you have any doubts about my answer, please leave a remark.

02

Vertex for Each Set

Assume the graph GV,E, which has a vertex for each person in the vertex set. If an edge e connects the vertices uandv, , it means that the person v is acquainted with the person u . So, in the induced network [where V ' is the new set of vertices], we may restrict the task to identifying a subset V of V whereby each vertex has a value more than 5 and less than|V'|-5 .

The continuous strategy can be used, in which all nodes are examined at first, and any node with a degree more than role="math" localid="1658920458569" |V'|-5orlessthan5 is eliminated. This graph is changed to be the induced graph, with the remaining vertices being assigned to the vertex set. This technique is repeated with the updated degrees for each node until a graph is formed in which no vertex may be deleted once the operation is completed. G' is the symbol for this graph. There are n iterations in the algorithm, and each iteration takes On time. As a result, the overall complexity of the running time is role="math" localid="1658920588246" O(n2).

03

Conclusion  

A vertex for each person in the vertex set like u and v means the person v is acquainted with the person u. So, identifying of sub set v where each vertex has value more than 5. same way this technique is repeated with the updated degrees for each node until a graph is form in which no vertex may deleted once the operation is complete. As a result overall complexity of the running time.

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Most popular questions from this chapter

The tramp steamer problem. You are the owner of a steamship that can apply between a group of port cities V . You make money at each port: a visit to city i earns you a profit of pi dollars. Meanwhile, the transportation cost from port i to port j is cij>0 .You want to find a cyclic route in which the ratio of profit to cost is maximized.

To this end, consider a directed graph G=(V,E) whose nodes are ports, and which has edges between each pair of ports. For any cycle C in this graph, the profit-to-cost ratio is

role="math" localid="1658920675878" r(c)=i,jicPiji,jicCij

Let r' be the maximum ratio achievable by a simple cycle. One way to determine r' is by binary search: by first guessing some ratio r , and then testing whether it is too large or too small. Consider any positive r>0 . Give each edge (i,j) a weight of wij=rcij-pj .

  1. Show that if there is a cycle of negative weight, then .
  2. Show that if all cycles in the graph have strictly positive weight, then r<r*.
  3. Give an efficient algorithm that takes as input a desired accuracy >0 and returns a simple cycle c for which r(C)3r*- Justify the correctness of your algorithm and analyze its running time in terms of |V|, and R=max(i,j)iE(PJCIJ) .

Show that, if c is a positive real number, then g(n) = 1 + c + c2 + · · · + cn is:

(a) Θ(1) if c < 1.

(b) Θ(n) if c = 1.

(c) Θ(cn) if c > 1.

The moral: in big-Θ terms, the sum of a geometric series is simply the first term if the series is strictly decreasing, the last term if the series is strictly increasing, or the number of terms if the series is unchanging.

Mean and median. One of the most basic tasks in statistics is to summarize a set of observations x1,x2,,xnR by a single number. Two popular choices for this summary statistic are:

• The median, which we’ll callμ1

• The mean, which we’ll callμ2

(a) Show that the median is the value of μthat minimizes the function

i|xi-μ|

You can assume for simplicity that is odd. (Hint: Show that for any , the function decreases if you move either slightly to the left or slightly to the right.)

(b) Show that the mean is the value of μ that minimizes the function

i(xi-μ)2

One way to do this is by calculus. Another method is to prove that for any μR,

i(xi-μ)2=i(xi-μ2)2+n(μ-μ2)2

Notice how the function for μ2 penalizes points that are far from much more heavily than the function for μ1 . Thus μ2 tries much harder to be close to all the observations. This might sound like a good thing at some level, but it is statistically undesirable because just a few outliers can severely throw off the estimate of μ2 . It is therefore sometimes said that μ1 is a more robust estimator than μ2 . Worse than either of them, however, is μ , the value of μthat minimizes the function

maxi|xi-μ|

(c) Show that μ can be computed in O(n) time (assuming the numbers are xismall enough that basic arithmetic operations on them take unit time).

Question: An Eulerian tourin an undirected graph is a cycle that is allowed to pass through each vertex multiple times, but must use each edge exactly once.

This simple concept was used by Euler in to solve the famous Konigsberg bridge problem, which launched the field of graph theory. The city of Konigsberg (now called Kaliningrad, in western Russia) is the meeting point of two rivers with a small island in the middle. There are seven bridges across the rivers, and a popular recreational question of the time was to determine whether it is possible to perform a tour in which each bridge is crossed exactly once. Euler formulated the relevant information as a graph with four nodes (denoting land masses) and seven edges (denoting bridges), as shown here.

Notice an unusual feature of this problem: multiple edges between certain pairs of nodes.

(a) Show that an undirected graph has an Eulerian tour if and only if all its vertices have even degree. Conclude that there is no Eulerian tour of the Konigsberg bridges.

(b) An Eulerian pathis a path which uses each edge exactly once. Can you give a similar if-and-only-if characterization of which undirected graphs have Eulerian paths?

(c) Can you give an analog of part (a) for directedgraphs?

There are many variants of Rudrata’s problem, depending on whether the graph is undirected or directed, and whether a cycle or path is sought. Reduce the DIRECTED RUDRATA PATH problem to each of the following.(a)The (undirected) RUDRATA PATH problem.(b) The undirected RUDRATA PATH problem, which is just like RUDRATA PATH except that the endpoints of the path are specified in the input.

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