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.

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

ja/codes/java/chapter_greedy/max_capacity.java

@@ -0,0 +1,38 @@
+/**
+ * File: max_capacity.java
+ * Created Time: 2023-07-21
+ * Author: krahets (krahets@163.com)
+ */
+
+package chapter_greedy;
+
+public class max_capacity {
+    /* 最大容量：貪欲法 */
+    static int maxCapacity(int[] ht) {
+        // i、j を初期化し、配列の両端で分割させる
+        int i = 0, j = ht.length - 1;
+        // 初期最大容量は 0
+        int res = 0;
+        // 2つの板が出会うまで貪欲選択をループ
+        while (i < j) {
+            // 最大容量を更新
+            int cap = Math.min(ht[i], ht[j]) * (j - i);
+            res = Math.max(res, cap);
+            // より短い板を内側に移動
+            if (ht[i] < ht[j]) {
+                i++;
+            } else {
+                j--;
+            }
+        }
+        return res;
+    }
+
+    public static void main(String[] args) {
+        int[] ht = { 3, 8, 5, 2, 7, 7, 3, 4 };
+
+        // 貪欲アルゴリズム
+        int res = maxCapacity(ht);
+        System.out.println("最大容量は " + res + " です");
+    }
+}