feat: add js solution to lcci problem: No.17.12

lcci/17.12.BiNode/README.md

@@ -157,6 +157,25 @@ func convertBiNode(root *TreeNode) *TreeNode {
 }
 ```
 
+```js
+const convertBiNode = root => {
+    const dfs = root => {
+        if (!root) {
+            return;
+        }
+        dfs(root.left);
+        prev.right = root;
+        root.left = null;
+        prev = root;
+        dfs(root.right);
+    };
+    const dummy = new TreeNode(0);
+    let prev = dummy;
+    dfs(root);
+    return dummy.right;
+};
+```
+
 <!-- tabs:end -->
 
 <!-- end -->

lcci/17.12.BiNode/README_EN.md

@@ -154,6 +154,25 @@ func convertBiNode(root *TreeNode) *TreeNode {
 }
 ```
 
+```js
+const convertBiNode = root => {
+    const dfs = root => {
+        if (!root) {
+            return;
+        }
+        dfs(root.left);
+        prev.right = root;
+        root.left = null;
+        prev = root;
+        dfs(root.right);
+    };
+    const dummy = new TreeNode(0);
+    let prev = dummy;
+    dfs(root);
+    return dummy.right;
+};
+```
+
 <!-- tabs:end -->
 
 <!-- end -->

lcci/17.12.BiNode/Solution.js

@@ -0,0 +1,16 @@
+const convertBiNode = root => {
+    const dfs = root => {
+        if (!root) {
+            return;
+        }
+        dfs(root.left);
+        prev.right = root;
+        root.left = null;
+        prev = root;
+        dfs(root.right);
+    };
+    const dummy = new TreeNode(0);
+    let prev = dummy;
+    dfs(root);
+    return dummy.right;
+};