docs: add Japanese translate documents (#1812)

* docs: add Japanese documents (`ja/docs`)

* docs: add Japanese documents (`ja/codes`)

* docs: add Japanese documents

* Remove pythontutor blocks in ja/

* Add an empty at the end of each markdown file.

* Add the missing figures (use the English version temporarily).

* Add index.md for Japanese version.

* Add index.html for Japanese version.

* Add missing index.assets

* Fix backtracking_algorithm.md for Japanese version.

* Add avatar_eltociear.jpg. Fix image links on the Japanese landing page.

* Add the Japanese banner.

---------

Co-authored-by: krahets <krahets@163.com>

ja/codes/cpp/utils/vertex.hpp

@@ -0,0 +1,36 @@
+/**
+ * File: vertex.hpp
+ * Created Time: 2023-03-02
+ * Author: krahets (krahets@163.com)
+ */
+
+#pragma once
+
+#include <vector>
+
+using namespace std;
+
+/* 頂点クラス */
+struct Vertex {
+    int val;
+    Vertex(int x) : val(x) {
+    }
+};
+
+/* 値のリストvals を入力し、頂点のリストvets を返す */
+vector<Vertex *> valsToVets(vector<int> vals) {
+    vector<Vertex *> vets;
+    for (int val : vals) {
+        vets.push_back(new Vertex(val));
+    }
+    return vets;
+}
+
+/* 頂点のリストvets を入力し、値のリストvals を返す */
+vector<int> vetsToVals(vector<Vertex *> vets) {
+    vector<int> vals;
+    for (Vertex *vet : vets) {
+        vals.push_back(vet->val);
+    }
+    return vals;
+}