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Showing posts with the label Algorithms

How to create Fibonacci series using Linq

In this post I am going to show you how to generate fiboancci number series using Linq.What is Fibonacci series : The Fibonacci Sequence is the series of numbers: 0, 1, 1, 2, 3, 5, 8, 13, 21, 34, ... The next number is found by adding up the two numbers before it. public static IEnumerable<int> Fib(int n) { List<int> fibs = new List<int>(); Enumerable.Range(0, n) .ToList() .ForEach(f => fibs.Add((f <= 1 ? 1 : fibs[f - 2] + fibs[f - 1]))); return fibs; }

Kth Largest Element in Array

publicclass KthElement { publicstaticint kthElement(int[] arr, int k) { int n = arr.Length; int lo = 0; int hi = n - 1; if (lo == hi) return arr[lo]; while (true) { int pivotIndex = Partition(arr, lo, hi); int rank = pivotIndex - lo + 1; if (rank == k) return arr[pivotIndex]; elseif (k < rank) return kthElement(arr, k); elsereturn kthElement(arr, k - rank); } } privatestaticint Partition(int[] arr, int left, int right) { int pivot = arr[left]; int i = left + 1; int j = right; while (i < j) { while (arr[i] <pivot) i++; while (arr[j] >= pivot) j--; if (i < j) Swap(arr, i, j); } Swap(arr, left, j); return j; } privatestaticvoid Swap(int[] arr, int i, int j) { int temp = arr[i]; arr[i] = arr[j]; …

Levenshtein distance (Edit distance)

The edit distance of two strings, s1 and s2, is defined as the minimum number of point mutations required to change s1 into s2, where a point mutation is one of:

change a letter,insert a letter, ordelete a letter



class EditDistanceAlgo { staticint[,] m; publicstaticchar diagCh; publicstaticint LevenshteinDistance(string s, string t) { int[,] d = newint[s.Length + 1, t.Length + 1]; for (int i = 0; i <= s.Length; i++) d[i, 0] = i; for (int j = 0; j <= t.Length; j++) d[0, j] = j; for (int j = 1; j <= t.Length; j++) for (int i = 1; i <= s.Length; i++) if (s[i - 1] == t[j - 1]) d[i, j] = d[i - 1, j - 1]; //no operationelse d[i, j] = Math.Min(Math.Min( d[i - 1, j] + 1, //a deletion d[i, j - 1] + 1), //an insertion d[i - 1, j - 1] +…

Longest increasing subsequence problem (Dynamic Programming)

The input consists of two sequences ~x = x1, . . . , xn and ~y = y1, . . . , ym. The goal is to find a longest common subsequence of ~x and ~y, that is a sequence z1, . . . , zk that is a subsequence both of ~x and of ~y. Note that a subsequence is not always substring: if ~z is a subsequence of ~x, and zi = xj and zi+1 = xj 0, then the only requirement is that j 0 > j, whereas for a substring it would have to be j 0 = j + 1.For example, let ~x and ~y be two DNA strings ~x = T GACT A and ~y = GT GCAT G; n = 6 and m = 7. Then one common subsequence would be GT A. However, it is not the longest possible common subsequence: there are common subsequences T GCA, T GAT and T GCT of length 4

0/1 Knapsack problem

Description

using System; publicclass Knapsack { staticint nbObjects = 8; staticint[] weight = { 2, 3, 5, 2, 4, 6, 3, 1 }; staticint[] utility = { 5, 8, 14, 6, 13, 17, 10, 4 }; staticint weightmax = 12; staticint[,] array; staticvoid Display() { int i, u, w; u = 0; w = weightmax; for (i = nbObjects - 1; i >= 1; i--) { if (array[i, w] != array[i - 1, w]) { Console.Write((i + 1) + " "); w = w - weight[i]; u = u + utility[i]; } } if (array[0, w] != 0) { Console.WriteLine("1"); w = w - weight[0]; u = u + utility[0]; } } publicstaticvoid SolveDP() { array = newint[nbObjects, weightmax + 1]; // initialize the first rowfor (int j = 0; j <= weightmax; j++) if (j < weight[0]) { arr…

Generate permutations of a given string in c#

In this post I will show you how to generate the permutations of a given string in c#.

Pseudocode:
If you have no more characters left to rearrange, print current permutation

for (every possible choice among the characters left to rearrange) { Make a choice and add that character to the permutation so far Use recursion to rearrange the remaining letters } using System.Collections.Generic; using System; using System.Generic; using System.Linq; using System.Text; namespace Permutation { class Program { staticvoid Main(string[] args) { Permutation("abc"); } /// <summary>/// Wrapper function/// </summary>/// <param name="input"></param>publicstaticvoid Permutation(string input) { RecPermutation("", input); } privatestaticvoid RecPermutation(string soFar, string input) { if (string.IsNullOrEmpty(input)) { …

Recursive merge sort implementation in c#

Merge Sort

using System; using System.Collections.Generic; using System.Linq; using System.Text; namespace MergeSort { publicclass Program { privateint[] originalArray; privateint[] resultArray; publicvoid MergeSort(int[] array) { this.originalArray = array; this.resultArray = newint[array.Length]; Merge(0, array.Length - 1); } privatevoid Merge(int low, int high) { if (low < high) { int middle = (low + high) / 2; Merge(low, middle); Merge(middle + 1, high); Sort(low, middle, high); } } /// <summary>/// Returns a new sorted list containing the same elements as L/// </summary>/// <param name="low"></param>/// <param name="middle"></param>/// <param name="high"></param>privatevoid Sort(int lo…

Quicksort implementation in c#

Quicksort is a very efficient sorting algorithm invented by C.A.R. Hoare. It has two phases:the partition phase andthe sort phase.Quicksort a good example of the divide and conquer strategy for solving problems. In quicksort, we divide the array of items to be sorted into two partitions and then call the quicksort procedure recursively to sort the two partitions, ie we divide the problem into two smaller ones and conquer by solving the smaller ones.

How to implement selection sort in c#

In this post I will show you how to implement selection sort in c#.Before going to implement selection sort let's describe how selection sort works.

go through the list one item at a time.keep track of the smallest item found.Find the smallest item out and add it to a list of sorted items.Repeat until all the items have been sorted



class Program { // Selection Sort Algorithmpublicstaticvoid SelectionSort(int[] arr) { int i, j; int min; for (i = 0; i < arr.Length - 1; i++) { min = i; for (j = i + 1; j < arr.Length; j++) { if (arr[j] < arr[min]) { min = j; } } Swap(arr, i, min); } } privatestaticvoid Swap(int[] arr, int i, int min) { int temp = arr[i]; arr[i] = arr[min]; arr[m…

Boyer-Moore search algorithm implementation in c#

Boyer-Mooreis a string searching algorithm. It avoids checking most positions in the source string. The implementation here uses constant characters.
publicclass Search { privatestaticint[] BuildBadCharTable(char[] needle) { int[] badShift = newint[256]; for (int i = 0; i < 256; i++) { badShift[i] = needle.Length; } int last = needle.Length - 1; for (int i = 0; i < last; i++) { badShift[(int)needle[i]] = last - i; } return badShift; } publicstaticint boyerMooreHorsepool(String pattern, String text) { char[] needle = pattern.ToCharArray(); char[] haystack = text.ToCharArray(); if (needle.Length > haystack.Length) { return -1; } int[] badShift = BuildBadCharTable(needle); int offset = 0; …

How to implement bubble sort in c#

In this post,I am going to show you how to implement bubble sorting in c#.
What is Bubble Sort
Bubble sort, is a simple sorting algorithm that works by repeatedly stepping through the list to be sorted, comparing each pair of adjacent items and swapping them if they are in the wrong order.
Implementation


using System; using System.Collections.Generic; using System.Linq; using System.Text; namespace SortingDemo { publicclass BubbleSort { publicvoid BubbleSort() { //Initialize array dataint[] data = { 5, 3, 6, 1, 8, 7, 2, 4 }; for (int outerIndex = 0; outerIndex < data.Length; outerIndex++) { for (int innerIndex = 0; innerIndex < data.Length-1; innerIndex++) { if (data[innerIndex] > data[innerIndex+1]) { //swap data. Swap(data, innerIndex); } } } } privatestaticvoid Swap(int[] dat…