Re-orgainze files and folders in the repository (#172)

* Re-orgainze files and folders in the repository

* updating DIRECTORY.md

Co-authored-by: github-actions <${GITHUB_ACTOR}@users.noreply.github.com>

Data-Structures/Array/QuickSelect.js

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+/**
+ * QuickSelect is an algorithm to find the kth smallest number
+ *
+ * Notes:
+ * -QuickSelect is related to QuickSort, thus has optimal best and average
+ *  case (O(n)) but unlikely poor worst case (O(n^2))
+ * -This implementation uses randomly selected pivots for better performance
+ *
+ * @complexity: O(n) (on average )
+ * @complexity: O(n^2) (worst case)
+ * @flow
+ */
+
+function QuickSelect (items, kth) {
+  return RandomizedSelect(items, 0, items.length - 1, kth)
+}
+
+function RandomizedSelect (
+  items,
+  left,
+  right,
+  i
+) {
+  if (left === right) return items[left]
+
+  const pivotIndex = RandomizedPartition(items, left, right)
+  const k = pivotIndex - left + 1
+
+  if (i === k) return items[pivotIndex]
+  if (i < k) return RandomizedSelect(items, left, pivotIndex - 1, i)
+
+  return RandomizedSelect(items, pivotIndex + 1, right, i - k)
+}
+
+function RandomizedPartition (items, left, right) {
+  const rand = getRandomInt(left, right)
+  Swap(items, rand, right)
+  return Partition(items, left, right)
+}
+
+function Partition (items, left, right) {
+  const x = items[right]
+  let pivotIndex = left - 1
+
+  for (let j = left; j < right; j++) {
+    if (items[j] <= x) {
+      pivotIndex++
+      Swap(items, pivotIndex, j)
+    }
+  }
+
+  Swap(items, pivotIndex + 1, right)
+
+  return pivotIndex + 1
+}
+
+function getRandomInt (min, max) {
+  return Math.floor(Math.random() * (max - min + 1)) + min
+}
+
+function Swap (arr, x, y) {
+  const temp = arr[x]
+  arr[x] = arr[y]
+  arr[y] = temp
+}
+
+// testing
+console.log(QuickSelect([1, 4, 2, -2, 4, 5]))

Data-Structures/Graph/Graph2.js

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+// create a graph class
+class Graph {
+  // defining vertex array and
+  // adjacent list
+  constructor (noOfVertices) {
+    this.noOfVertices = noOfVertices
+    this.AdjList = new Map()
+  }
+
+  // functions to be implemented
+
+  // addVertex(v)
+  // addEdge(v, w)
+  // printGraph()
+
+  // bfs(v)
+  // dfs(v)
+
+  // add vertex to the graph
+  addVertex (v) {
+    // initialize the adjacent list with a
+    // null array
+
+    this.AdjList.set(v, [])
+  }
+
+  // add edge to the graph
+  addEdge (v, w) {
+    // get the list for vertex v and put the
+    // vertex w denoting edge between v and w
+    this.AdjList.get(v).push(w)
+
+    // Since graph is undirected,
+    // add an edge from w to v also
+    this.AdjList.get(w).push(v)
+  }
+
+  // Prints the vertex and adjacency list
+  printGraph () {
+    // get all the vertices
+    const getKeys = this.AdjList.keys()
+
+    // iterate over the vertices
+    for (const i of getKeys) {
+      // great the corresponding adjacency list
+      // for the vertex
+      const getValues = this.AdjList.get(i)
+      let conc = ''
+
+      // iterate over the adjacency list
+      // concatenate the values into a string
+      for (const j of getValues) {
+        conc += j + ' '
+      }
+
+      // print the vertex and its adjacency list
+      console.log(i + ' -> ' + conc)
+    }
+  }
+}
+// Example
+const graph = new Graph(6)
+const vertices = ['A', 'B', 'C', 'D', 'E', 'F']
+
+// adding vertices
+for (let i = 0; i < vertices.length; i++) {
+  graph.addVertex(vertices[i])
+}
+
+// adding edges
+graph.addEdge('A', 'B')
+graph.addEdge('A', 'D')
+graph.addEdge('A', 'E')
+graph.addEdge('B', 'C')
+graph.addEdge('D', 'E')
+graph.addEdge('E', 'F')
+graph.addEdge('E', 'C')
+graph.addEdge('C', 'F')
+
+// prints all vertex and
+// its adjacency list
+// A -> B D E
+// B -> A C
+// C -> B E F
+// D -> A E
+// E -> A D F C
+// F -> E C
+graph.printGraph()