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/java/chapter_hashing/simple_hash.java

@@ -0,0 +1,65 @@
+/**
+ * File: simple_hash.java
+ * Created Time: 2023-06-21
+ * Author: krahets (krahets@163.com)
+ */
+
+package chapter_hashing;
+
+public class simple_hash {
+    /* 加算ハッシュ */
+    static int addHash(String key) {
+        long hash = 0;
+        final int MODULUS = 1000000007;
+        for (char c : key.toCharArray()) {
+            hash = (hash + (int) c) % MODULUS;
+        }
+        return (int) hash;
+    }
+
+    /* 乗算ハッシュ */
+    static int mulHash(String key) {
+        long hash = 0;
+        final int MODULUS = 1000000007;
+        for (char c : key.toCharArray()) {
+            hash = (31 * hash + (int) c) % MODULUS;
+        }
+        return (int) hash;
+    }
+
+    /* XORハッシュ */
+    static int xorHash(String key) {
+        int hash = 0;
+        final int MODULUS = 1000000007;
+        for (char c : key.toCharArray()) {
+            hash ^= (int) c;
+        }
+        return hash & MODULUS;
+    }
+
+    /* 回転ハッシュ */
+    static int rotHash(String key) {
+        long hash = 0;
+        final int MODULUS = 1000000007;
+        for (char c : key.toCharArray()) {
+            hash = ((hash << 4) ^ (hash >> 28) ^ (int) c) % MODULUS;
+        }
+        return (int) hash;
+    }
+
+    public static void main(String[] args) {
+        String key = "Hello algorithm";
+
+        int hash = addHash(key);
+        System.out.println("加算ハッシュ値は " + hash + " です");
+
+        hash = mulHash(key);
+        System.out.println("乗算ハッシュ値は " + hash + " です");
+
+        hash = xorHash(key);
+        System.out.println("XORハッシュ値は " + hash + " です");
+
+        hash = rotHash(key);
+        System.out.println("回転ハッシュ値は " + hash + " です");
+    }
+}