merge: Add Graph3 (add DFS in Iterative Way) (#944)

* Add Graph3 (add DFS in Iterative Way)

* Remove example code and add test code (Graph3)

* Remove redundant code (like return undefined)

Data-Structures/Graph/Graph3.js

@@ -0,0 +1,108 @@
+class Graph {
+  constructor () {
+    this.adjacencyObject = {}
+  }
+
+  addVertex (vertex) {
+    if (!this.adjacencyObject[vertex]) this.adjacencyObject[vertex] = []
+  }
+
+  addEdge (vertex1, vertex2) {
+    this.adjacencyObject[vertex1].push(vertex2)
+    this.adjacencyObject[vertex2].push(vertex1)
+  }
+
+  removeEdge (vertex1, vertex2) {
+    this.adjacencyObject[vertex1] = this.adjacencyObject[vertex1].filter(
+      (v) => v !== vertex2
+    )
+    this.adjacencyObject[vertex2] = this.adjacencyObject[vertex2].filter(
+      (v) => v !== vertex1
+    )
+  }
+
+  removeVertex (vertex) {
+    while (this.adjacencyObject[vertex].length) {
+      const adjacentVertex = this.adjacencyObject[vertex].pop()
+      this.removeEdge(vertex, adjacentVertex)
+    }
+  }
+
+  /**
+   * Return DFS (Depth First Search) List Using Recursive Method
+   */
+  DFS (start) {
+    if (!start) return null
+
+    const result = []
+    const visited = {}
+    const adjacencyObject = this.adjacencyObject
+
+    function dfs (vertex) {
+      if (!vertex) return null
+      visited[vertex] = true
+      result.push(vertex)
+      adjacencyObject[vertex].forEach((neighbor) => {
+        if (!visited[neighbor]) {
+          dfs(neighbor)
+        }
+      })
+    }
+
+    dfs(start)
+    return result
+  }
+
+  /**
+   * Return DFS(Depth First Search) List Using Iteration
+   */
+  DFSIterative (start) {
+    if (!start) return null
+
+    const stack = [start]
+    const visited = {}
+    visited[start] = true
+
+    const result = []
+    let currentVertex
+
+    while (stack.length) {
+      currentVertex = stack.pop()
+      result.push(currentVertex)
+
+      this.adjacencyObject[currentVertex].forEach((neighbor) => {
+        if (!visited[neighbor]) {
+          visited[neighbor] = true
+          stack.push(neighbor)
+        }
+      })
+    }
+    return result
+  }
+
+  BFS (start) {
+    if (!start) return null
+
+    const queue = [start]
+    const visited = {}
+    visited[start] = true
+
+    let currentVertex
+    const result = []
+
+    while (queue.length) {
+      currentVertex = queue.shift()
+      result.push(currentVertex)
+
+      this.adjacencyObject[currentVertex].forEach((neighbor) => {
+        if (!visited[neighbor]) {
+          visited[neighbor] = true
+          queue.push(neighbor)
+        }
+      })
+    }
+    return result
+  }
+}
+
+export { Graph }