- Design and Analysis of Algorithms
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- Basics of Algorithms
- DAA - Introduction
- DAA - Analysis of Algorithms
- DAA - Methodology of Analysis
- Asymptotic Notations & Apriori Analysis
- DAA - Space Complexities

- Design Strategies
- DAA - Divide & Conquer
- DAA - Max-Min Problem
- DAA - Merge Sort
- DAA - Binary Search
- Strassen’s Matrix Multiplication
- DAA - Greedy Method
- DAA - Fractional Knapsack
- DAA - Job Sequencing with Deadline
- DAA - Optimal Merge Pattern
- DAA - Dynamic Programming
- DAA - 0-1 Knapsack
- Longest Common Subsequence

- Graph Theory
- DAA - Spanning Tree
- DAA - Shortest Paths
- DAA - Multistage Graph
- Travelling Salesman Problem
- Optimal Cost Binary Search Trees

- Heap Algorithms
- DAA - Binary Heap
- DAA - Insert Method
- DAA - Heapify Method
- DAA - Extract Method

- Sorting Methods
- DAA - Bubble Sort
- DAA - Insertion Sort
- DAA - Selection Sort
- DAA - Quick Sort
- DAA - Radix Sort

- Complexity Theory
- Deterministic vs. Nondeterministic Computations
- DAA - Max Cliques
- DAA - Vertex Cover
- DAA - P and NP Class
- DAA - Cook’s Theorem
- NP Hard & NP-Complete Classes
- DAA - Hill Climbing Algorithm

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- DAA - Quick Guide
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- DAA - Discussion

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Merge a set of sorted files of different length into a single sorted file. We need to find an optimal solution, where the resultant file will be generated in minimum time.

If the number of sorted files are given, there are many ways to merge them into a single sorted file. This merge can be performed pair wise. Hence, this type of merging is called as **2-way merge patterns**.

As, different pairings require different amounts of time, in this strategy we want to determine an optimal way of merging many files together. At each step, two shortest sequences are merged.

To merge a **p-record file** and a **q-record file** requires possibly **p + q** record moves, the obvious choice being, merge the two smallest files together at each step.

Two-way merge patterns can be represented by binary merge trees. Let us consider a set of **n** sorted files **{f _{1}, f_{2}, f_{3}, …, f_{n}}**. Initially, each element of this is considered as a single node binary tree. To find this optimal solution, the following algorithm is used.

Algorithm: TREE (n)for i := 1 to n – 1 do declare new node node.leftchild := least (list) node.rightchild := least (list) node.weight) := ((node.leftchild).weight) + ((node.rightchild).weight) insert (list, node); return least (list);

At the end of this algorithm, the weight of the root node represents the optimal cost.

Let us consider the given files, f_{1}, f_{2}, f_{3}, f_{4} and f_{5} with 20, 30, 10, 5 and 30 number of elements respectively.

If merge operations are performed according to the provided sequence, then

**M _{1} = merge f_{1} and f_{2}** => 20 + 30 = 50

**M _{2} = merge M_{1} and f_{3}** => 50 + 10 = 60

**M _{3} = merge M_{2} and f_{4}** => 60 + 5 = 65

**M _{4} = merge M_{3} and f_{5}** => 65 + 30 = 95

Hence, the total number of operations is

50 + 60 + 65 + 95 = 270

Now, the question arises is there any better solution?

Sorting the numbers according to their size in an ascending order, we get the following sequence −

**f _{4}, f_{3}, f_{1}, f_{2}, f_{5}**

Hence, merge operations can be performed on this sequence

**M _{1} = merge f_{4} and f_{3}** => 5 + 10 = 15

**M _{2} = merge M_{1} and f_{1}** => 15 + 20 = 35

**M _{3} = merge M_{2} and f_{2}** => 35 + 30 = 65

**M _{4} = merge M_{3} and f_{5}** => 65 + 30 = 95

Therefore, the total number of operations is

15 + 35 + 65 + 95 = 210

Obviously, this is better than the previous one.

In this context, we are now going to solve the problem using this algorithm.

Hence, the solution takes 15 + 35 + 60 + 95 = 205 number of comparisons.

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