CSC645 Algorithm Analysis Chapter 3
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Questions and Answers

When analyzing the time efficiency of recursive algorithms, the initial step involves solving the recurrence for the order of growth of its solution.

False (B)

A recurrence relation of $T(n) = T(n-1) + 1$ corresponds to an algorithm with $O(log n)$ time complexity.

False (B)

The recurrence relation $T(n) = 2T(n/2) + 1$ is representative of the time complexity of a tree traversal algorithm.

True (A)

For a recurrence relation $T(n) = T(n-k) + k$, if $k = n + 1$, then $T(n) = T(1) + n + 1$.

<p>False (B)</p> Signup and view all the answers

If an algorithm has a recurrence relation of $T(n) = 2T(n/2) + n$, its time complexity is $O(n^2)$.

<p>False (B)</p> Signup and view all the answers

In analyzing the time efficiency of an iterative algorithm, the first step is to pinpoint the algorithm's least significant operation.

<p>False (B)</p> Signup and view all the answers

When analyzing algorithms, the best-case scenario provides an upper bound on the algorithm's performance.

<p>False (B)</p> Signup and view all the answers

The summation $\sum_{i=0}^{n} i$ simplifies to $\frac{n(n+1)}{2}$.

<p>True (A)</p> Signup and view all the answers

If an algorithm's time complexity is expressed as $\frac{n^2 - 7n + 4}{2}$, it belongs to $\Theta(n^3)$.

<p>False (B)</p> Signup and view all the answers

In Example 1, the outer loop iterates from $i = 0$ to $n-1$, and the inner loop iterates from $j = i+1$ to $n-1$, with a constant time operation inside. The time complexity is $\Theta(n)$.

<p>False (B)</p> Signup and view all the answers

In the binary representation formula $b = (\log_2 n) + 1$, 'b' represents the base of the logarithm.

<p>False (B)</p> Signup and view all the answers

When analyzing iterative algorithms that repeatedly halve the input size, a logarithmic time complexity, $O(\log n)$, is often observed.

<p>True (A)</p> Signup and view all the answers

The time complexity of an algorithm where the value of n is halved on each repetition of a loop is $O(n\log n)$.

<p>False (B)</p> Signup and view all the answers

Flashcards

Empirical Analysis

A method of algorithm analysis based on practical experiments and measurements.

Iterative Algorithms

Algorithms that repeat a sequence of operations until a condition is met.

Recursive Algorithms

Algorithms that solve a problem by breaking it down into smaller subproblems of the same type.

Time Efficiency

A measure of the amount of time an algorithm takes to execute as a function of input size.

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Basic Operation

The most significant operation in an algorithm that affects its efficiency.

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Summation Formula

A mathematical expression used to summarize the running time of an algorithm.

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O(log n)

Big O notation representing logarithmic time complexity.

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Algorithm Analysis Steps

A structured approach involving deciding parameters, identifying operations, finding sums, and simplifying.

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Recurrence Relation

An equation that recursively defines a sequence of values.

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Time Complexity

A computational complexity that describes the amount of time an algorithm takes to complete.

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Binary Search

An algorithm that finds an item in a sorted array by repeatedly dividing the search interval in half.

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Merge Sort

A divide-and-conquer algorithm that sorts data by dividing it into smaller segments and merging them back in order.

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Selection Sort

A simple comparison-based sorting algorithm that divides the input into a sorted and an unsorted region.

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Study Notes

Algorithm Analysis & Design

  • Course: CSC645
  • Chapter 3: Methods of Algorithm Analysis
  • Author: Nur Azmina Mohamad Zamani

Chapter Overview

  • Analysis of iterative algorithms
  • Analysis of recursive algorithms
  • Includes empirical analysis

Time Efficiency of Iterative Algorithms

  • General Plan for Analysis
    • Decide on parameter n, indicating input size
    • Identify algorithm's basic operation
    • Determine worst, average and best cases for input of size n
    • Set up a sum for the number of times the basic operation is executed
    • Simplify the sum using standard formulas and rules

Summation Formulas & Rules

  • Σcaᵢ = cΣaᵢ (R1)
  • Σ(aᵢ + bᵢ) = Σaᵢ + Σbᵢ (R2)
  • Σi = 1 = n(n+1) /2 ≈ n² (S2)
  • Where i ∈ {1, 2... n}

Summation Formula of i

  • Multiple summation formulas for different powers of i given

Example 1: Unique Elements

  • Algorithm: Identifies whether all elements in an array are distinct
    • Input: Array A[0..n-1]
    • Output: True if distinct, False otherwise
    • Nested loops examine all pairs of elements for equality
    • Time complexity using summation notation is shown

Solution for Example 1

  • Calculation of the summation involved is shown leading to time complexity of θ(n²)

Exercises

  • Multiple exercises are present

Example 2: Binary Algorithm

  • Algorithm calculates the number of binary digits in a decimal integer.
    • Input: Positive decimal integer n
    • Output: Number of binary digits
    • The algorithm repeatedly divides by 2, incrementing a count with each division

Solution for Example 2

  • Algorithm steps involved
  • Time complexity is θ(log n)

Time Efficiency of Recursive Algorithms

  • General Plan for Analysis
    • Decide on parameter n, indicating input size
    • Identify algorithm's basic operation
    • Determine worst, average and best cases for input of size n
    • Set up recurrence relation for the number of times the basic operation is executed
    • Solve the recurrence for the order of growth of the solution

Recurrence Relation for Some Algorithms

  • Provides examples of recurrence relations (e.g. Binary search, Sequential search, Tree Traversal, Selection sort, Merge sort, Quick sort) and their corresponding Big-Oh solutions

Example 1 (Recurrence Relation)

  • Describes an algorithm with recurrence relation T(n) = T(n - 1) + 1, T(1) = 0
  • Solves the recurrence relation to find algorithm complexity θ(n)

Example 2 (Recurrence Relation)

  • Algorithm with recurrence relation T(n) = 2T(n/2) + n, T(1) = 1
  • Solves the recurrence showing time complexity θ(n log n)

Reference

  • Reference provided on algorithm analysis

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Description

Explore the methods of algorithm analysis in Chapter 3 of CSC645. This quiz covers the analysis of iterative and recursive algorithms, including techniques for empirical analysis and summation formulas. Test your understanding of time efficiency and algorithm performance.

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