JavaScript tree traversal: updated dfsInorder (#902)

Author: henrikac

CONTRIBUTORS.md

@@ -60,3 +60,4 @@ This file lists everyone, who contributed to this repo and wanted to show up her
 - Ridham177
 - Hugo Salou
 - Dimitri Belopopsky
++ Henrik Abel Christensen

contents/tree_traversal/code/javascript/tree.js

@@ -10,11 +10,19 @@ function createTree(rows, children) {
 }
 
 function dfsPreorder(tree) {
+  if (!tree) {
+    return;
+  }
+
   console.log(tree.id);
   tree.children.forEach(dfsPreorder);
 }
 
 function dfsPostorder(tree) {
+  if (!tree) {
+    return;
+  }
+
   tree.children.forEach(dfsPostorder);
   console.log(tree.id);
 }
@@ -24,13 +32,22 @@ function dfsInorder(tree) {
     return;
   }
 
-  if (tree.children.length > 2) {
-    throw new Error("Postorder traversal is only valid for binary trees");
+  switch (tree.children.length) {
+    case 2:
+      dfsInorder(tree.children[0]);
+      console.log(tree.id);
+      dfsInorder(tree.children[1]);
+      break;
+    case 1:
+      dfsInorder(tree.children[0]);
+      console.log(tree.id);
+      break;
+    case 0:
+      console.log(tree.id);
+      break;
+    default:
+      throw new Error("Postorder traversal is only valid for binary trees");
   }
-
-  dfsInorder(tree.children[0]);
-  console.log(tree.id);
-  dfsInorder(tree.children[1]);
 }
 
 function dfsIterative(tree) {

contents/tree_traversal/tree_traversal.md

@@ -62,7 +62,7 @@ Because of this, the most straightforward way to traverse the tree might be recu
 {% sample lang="java" %}
 [import:20-26, lang:"java"](code/java/Tree.java)
 {% sample lang="js" %}
-[import:12-15, lang:"javascript"](code/javascript/tree.js)
+[import:12-19, lang:"javascript"](code/javascript/tree.js)
 {% sample lang="py" %}
 [import:18-23, lang:"python"](code/python/Tree_example.py)
 {% sample lang="scratch" %}
@@ -118,7 +118,7 @@ Now, in this case the first element searched through is still the root of the tr
 {% sample lang="java" %}
 [import:33-40, lang:"java"](code/java/Tree.java)
 {% sample lang="js" %}
-[import:17-20, lang:"javascript"](code/javascript/tree.js)
+[import:21-28, lang:"javascript"](code/javascript/tree.js)
 {% sample lang="py" %}
 [import:26-31, lang:"python"](code/python/Tree_example.py)
 {% sample lang="scratch" %}
@@ -169,7 +169,7 @@ In this case, the first node visited is at the bottom of the tree and moves up t
 {% sample lang="java" %}
 [import:47-64, lang:"java"](code/java/Tree.java)
 {% sample lang="js" %}
-[import:22-34, lang:"javascript"](code/javascript/tree.js)
+[import:30-51, lang:"javascript"](code/javascript/tree.js)
 {% sample lang="py" %}
 [import:34-46, lang:"python"](code/python/Tree_example.py)
 {% sample lang="scratch" %}
@@ -229,7 +229,7 @@ In code, it looks like this:
 {% sample lang="java" %}
 [import:67-81, lang:"java"](code/java/Tree.java)
 {% sample lang="js" %}
-[import:36-43, lang:"javascript"](code/javascript/tree.js)
+[import:53-60, lang:"javascript"](code/javascript/tree.js)
 {% sample lang="py" %}
 [import:49-60, lang:"python"](code/python/Tree_example.py)
 {% sample lang="scratch" %}
@@ -282,7 +282,7 @@ And this is exactly what Breadth-First Search (BFS) does! On top of that, it can
 {% sample lang="java" %}
 [import:83-97, lang:"java"](code/java/Tree.java)
 {% sample lang="js" %}
-[import:45-52, lang:"javascript"](code/javascript/tree.js)
+[import:62-69, lang:"javascript"](code/javascript/tree.js)
 {% sample lang="py" %}
 [import:63-75, lang:"python"](code/python/Tree_example.py)
 {% sample lang="scratch" %}