Questions tagged [amortized-analysis]
A method in analysis of algorithms that considers the overall cost of a sequence of operations.
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Can there exist a deque like data structure that supports amortized $O(1)$ random access?
A lot of modern languages usually have a "list" or "vector" structure which allows for amortized $O(1)$ append and removal from back as well as amortized $O(1)$ random access.
I'm ...
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Exercise C-1.3 in Algorithm design and applications
There is a exercise in Algorithm design and applications (Goodrich) that I don't understand. It says:
What is the amortized running time of the operations in a sequence of n operations $P=p_1p_2 \...
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Amortized cost for Stack Operations
In this problem we consider two stacks $A$ and $B$
manipulated using the following operations ($n$ denotes the size of $A$ and $m$ the size of $B$):
PushA($x$): Push element $x$
on stack $A$.
...
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Amortized analysis of dynamic array insertion
I learned the amortized analysis of Prof Demaine's 6.006 videos. The Erik's thesis was, If we reallocate memory by doubling capacity => $$1 +2+4 + 8 + 16 +..+n = \theta(2^{lgn}) = \theta(n)$$ From ...
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Amortised cost - transferring tokens
I'm trying to solve a problem from one of the older exams.
Question:
There's an infinite, one-dimensional board, with fields numbered consecutively $\ldots, -2, -1, 0, 1, 2, \ldots$
A move in the ...
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Amortized analysis on skew heap arbitrary deletion
A practice problem in my textbook asks to proof the amortized complexity for a sequence of insert, delete min, and decrease-key operations on an initially empty skew heap. Insert and delete min both ...
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Prove with potential method that dynamic table with $q > 1$ expansion runs in amortized constant time
Suppose I have a dynamic table supporting $Insert$ procedure, which sets an input value after the tail of the dynamic table. If the underlying table is already full, we multiply its size by $q > 1$....
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Understanding David Pisinger's balanced algorithm for the subset-sum problem with bounded weights
I'm trying to understand David Pisinger's balanced algorithm for the subset-sum problem with bounded weights, which can be found on page 5 of his paper Linear Time Algorithms for Knapsack Problems ...
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Splay Trees - Sequential Access Theorem & lower bound for comparison-based sorting
The following theorem was proven by R.E. Tarjan in 1984:
Theorem (Sequential Access Theorem). If we access each of the nodes of an arbitrary initial tree once, in symmetric order, the total time ...
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Difficulty in last sentence in proof of "Amortized cost of $\text{Find-Set}$ operation is $O(\alpha(n))$" from CLRS
I was reading the section of Data Structures for Disjoint Sets from the text Introduction to Algorithms by Cormen et. al. I made it through the proof, but I'm not sure I understand the very last ...
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Finding the Equation for Potential Method and Amortization Analysis
I am trying to figure out the solution to this problem:
In this problem we consider two stacks $A$ and $B$ manipulated using the
following operations ($n$ denotes the size of $A$ and $m$ the size of $...
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Aggregate method for dynamic table (amortized analysis)
For amortized analysis (aggregate method), dynamic table insertion cost can be divided into:
if no expansion, then cost = 1
if we expand the table, then cost = i (if i-1 is an exact power of 2)
then ...
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What are the actual costs $c_i$ in the potential method?
In "Introduction to Algorithms" by Cormen et al. the Potential Method is explained. For example, we have the following representation for the amortized costs of the i-th operation with ...
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Algorithm for an incremental update to cut vertex set
There is a classic linear algorithm to find every cut vertex (AKA articulation point) in a graph.
I have a usecase that does this computation after every time a non-articulation-point is inserted or ...
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Designing a Data Structure that allows both insertion and extracting a number lower than median in amoritzed O(1) cost?
Consider a data structure that has only two functions. extract_lowerthan_median() and insert(). How can we design it in a way that the amortized cost for both the operation is O(1)?
Using a 2 tree, a ...
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Potential Method For Decimal Counter
There is a counter that counts the number of items in the store. For every increase in item or item that has been inserted, the cost is a + kb where k is the number of digits that has been changed in ...
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Prove: Self-organizing list that uses Move-to-Front is 2-Competitive
Preparing for my finals in my "advances algorithms" course. Usually there is a question to prove one of the theorems that was given over the course. I'm currently trying to write a full ...
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Algorithm with amortized time complexity
While I understand the process of considering/observing an algorithm and finding an average time, necessary to perform an operation that happens in this algorithm, I still cannot quite gasp the idea, ...
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Priority Queues with $DecreaseKey,FindMin,Insert$ in time $O(1)$, $DeleteMin$ in $ O(\log n)$ and $IncreaseKey$ in $O(1)$, Amortized
Problem:
In this problem, we discuss Data-Structures that maintain a group of ordered elements.
We must support the operations $ DecreaseKey, FindMin, Insert $ in time $ O(1) $ and the operation $ ...
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What is the amortized cost of pulling top K elements from a priority queue?
To pop an element off of a priority queue, the worst-case complexity is:
O(logN) where N is the number of elements.
Now if you do K pop operations on the priority ...
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Amortized analysis on a dynamic table that grows its size by $\sqrt{size} $
The following problem is based on the section about dynamic table as part of the discussion about amortized analysis in CLRS
Problem: We are given a dynamic table $T$ that supports INSERT operation, ...
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Cost of increasing a binary counter with a starting value n times
Consider a k-bit binary counter and suppose that in the beginning the value of the i-th most significant bit is $b_i$ for each $i = 0, . . . , k − 1$. Let $b = b_0 + 2b_1 +· · · + 2^{k−1}
b_{k−1}$. ...
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Amortized analysis (accounting/banker's method) for tree operations
Suppose we have a tree data structure with root $r$ with two operations:
Add($x, y$) - adds the node $y$ as a child to the node $x$
Zip($x$)- this makes the node $x$ and all of $x$'s ancenstors direct ...
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What is the meaning of the statement "a sequence of n PUSH, POP and MULTIPOP opreations"
I am reading CLRS 3rd Ed, chapter 17.1 (Aggregate analysis pg453) and I came across this statement.
Let us analyze a sequence of n PUSH, POP, and MULTIPOP operations on an initially
empty stack.
I ...
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Amortized Analysis of extract-min-operation of Fibonacci Heap
I am studying the operations of the Fibonacci heap. While going through min-extraction operation every step and its complexities are fairly clear to me. In short, it is:
The potential before ...
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Analyzing Hybrid Merge and Insertion Sort
We know that merge sort takes O(n log n) and insertion sort takes (n^2) for worst case.
The combination of these two algorithm is to speed up and reduce key comparisons, as for a subarray with small ...
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Amortized cost depending on the number of operations
Considering a dynamic array that grows by a constant factor $k$ (the new array has $k$ more cells than the last one) each time the array is full which initially has $n$ elements in it. Calculating the ...
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A formal definition for amortized time
Several (tutoring) students have asked me for a formal definition of amortized time and I've never been able to find one online. All the literature I've found usually outlines the three most common ...
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General Proof on Potential Method and Amortized Analysis
Let $T$ be an arbitrary data structure for a dynamic set. For every state T of $T$, let $d_t \in \mathbb{N}$. Observe two Operations $O_1, O_2$ on $T$ whose runtimes are proportional to $d_t$ and $...
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Changing binary counter structure such that increament and decreament methods will work in O(1) amortized
Just trying to solve the second part of a question with two parts.
First part was to prove that you can't add decrement method to a standart binary counter without hurting the amortized complexity and ...
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Accounting method - dynamic array
I want to compute the amortize time of a type of dynamic array (inserting such that if i have no place to insert i am multipling the array by (1+a) (a is between 0 to 1).
I need to compute the time ...
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Amortized analysis - adding operations to a data structure
One of the finer points of amortized analysis about which I have been able to find relatively little information is the broad question of what happens to the amortized cost of a structure's existing ...
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Does this data structure already exist?
I was working on a problem for some time now, and I made a data structure to solve it. To my surprise, I could not find any instance of this data structure on the internet (though I am certain someone ...
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Can you delete-min from fibonacci heap in O(1) amortized?
I just had a data-structures exam. One of the questions asked us to create a data structure which allowed insert operations in O(logn) amortized and delete-max (or min, doesn't matter) in O(1) ...
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Fibonacci Heap that consolidates after every step
The lecturer of my graduate algorithms course suggested that, even if a Fibonacci Heap would consolidate its tree list after every operation (not just when doing deleteMin()), most operations would ...
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Dynamic array with 4x growth factor: Potential Method
I am curious on the use of the potential method for amortized analysis for a dynamic array which quadruples in size after it becomes full.
I understand how the potential function is defined and used ...
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design a strange data structure, is it possible?
I need a FIFO QUEUE that can do Insert and Remove from Queue in amortized $O(1)$ but extract min in $O(log n)$. is it possible?
When just find min is important (not removing) there is lots of $O(1)$ ...
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When do you use amortized time complexity and when to use unamortized?
This is my guess:
-Use amortized because we want to know the "averaged" complexity over n operations assuming the ...
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Create a potential function for an abstract queue data structure to show constant amortized-time complexity
Consider a variation of a Queue called MaxQueue, Q, that has the following operations:
dequeue(Q): removes and returns the first element of Q
enqueue(Q, s): Appends the integer s to the end of Q
...
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Closest point in embedded simplicial complex
Suppose I have a simplicial $k$-complex $\mathcal S$ whose vertices are embedded in Euclidean space $\mathbb R^n$, for roughly $k< n\leq 6$. Examples include triangle mesh surfaces ($k=2$) embedded ...
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Difficulty in few steps in proof of "Amortized cost of $\text{Find-Set}$ operation is $\Theta(\alpha(n))$"assuming union by rank, path compression
I was reading the section of data structures for disjoint sets from the text Introduction to Algorithms by Cormen et. al .I faced difficulty in understanding few steps in the proof of the lemma as ...
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Intuition behind the entire (amortized) concept of Fibonacci Heap operations
The following excerpts are from the section Fibonacci Heap from the text Introduction to Algorithms by Cormen et. al
The potential function for the Fibonacci Heaps $H$ is defined as follows:
$$\Phi(H)...
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Splay tree amortized analysis cost using Access Lemma
Currently studying for an algorithms exam and I came across this question and solution, but I can't understand the solution where it references nodes of depth less than $4\log n$ and not restructuring....
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$\Phi_1=1$ or $\Phi_1=2$ for the dynamic $\text{Table-Insert}$ , where $\Phi_i$ is the potential function after $i$ th operation, as per CLRS
The following comes from section Dynamic Tables, Introduction to Algorithms by Cormen. et. al.
In the following pseudocode, we assume that $T$ is an object representing the table. The field $table[T]$...
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Is there a known way to make an efficient, compact, and fully persistent stack or queue?
In the world of mutable/ephemeral data structures and imperative programming languages, one of the classic ways to implement a stack or queue is to use array doubling: use mutation to fill up or empty ...
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Amortized time for dynamic array
I'm struggling to understand one part from the book "Cracking the coding interview".
The author states inserting an element in a dynamic array is $O(1)$ most of the time, except when the array is full ...
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Amortized analysis for disjoint sets' find-set(x) function (from CLRS)
I start off by apologizing for the fact that I don't really know how to use latex/markdown. My question, however, is directly from the Introduction To Algorithms book by Cormen et al. The topic ...
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Does amortized algorithm analysis make any assumptions about the sequence of function calls?
I have read that average case analysis makes some assumptions about the inputs to the data structure, and amortized analysis makes no such assumptions.
Does amortized analysis make any assumptions ...
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Is using Fibonacci Heaps in Huffman Code, better than a regular Min-heap?
When using Huffman Code, to generate prefix-code trees for a sequence of letters, CLRS choose to use a normal Min-heap data structure.
Using Fibonacci-heaps instead, are we not able to achieve a ...
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Amortized value of dequeue with potential function
A deque is implemented with 3 stacks. one for the head, one for the tail and one is always empty.
Pushing is therefor O(1), light popping (in case the head/tail respectively aren't empty) is also O(1)....
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