Added cloneGraph solution

Author: nhistory

clone-graph/nhistory.js

@@ -0,0 +1,33 @@
+/**
+ * // Definition for a _Node.
+ * function _Node(val, neighbors) {
+ *    this.val = val === undefined ? 0 : val;
+ *    this.neighbors = neighbors === undefined ? [] : neighbors;
+ * };
+ */
+
+/**
+ * @param {_Node} node
+ * @return {_Node}
+ */
+var cloneGraph = function (node) {
+  let visited = {};
+
+  const dfs = (node) => {
+    if (!node) return node;
+    if (visited[node.val]) return visited[node.val];
+
+    let root = new Node(node.val);
+    visited[node.val] = root;
+
+    for (let neighbor of node.neighbors) {
+      root.neighbors.push(dfs(neighbor));
+    }
+    return root;
+  };
+
+  return dfs(node);
+};
+
+// TC: O(n+e) -> n: number of nodes | e: number of edges
+// SC: O(v) -> v: length of visited object