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_dynamic_programming/climbing_stairs_backtrack.java

@@ -0,0 +1,44 @@
+/**
+ * File: climbing_stairs_backtrack.java
+ * Created Time: 2023-06-30
+ * Author: krahets (krahets@163.com)
+ */
+
+package chapter_dynamic_programming;
+
+import java.util.*;
+
+public class climbing_stairs_backtrack {
+    /* バックトラッキング */
+    public static void backtrack(List<Integer> choices, int state, int n, List<Integer> res) {
+        // n段目に到達したとき、解の数に1を加える
+        if (state == n)
+            res.set(0, res.get(0) + 1);
+        // すべての選択肢を走査
+        for (Integer choice : choices) {
+            // 剪定：n段を超えて登ることを許可しない
+            if (state + choice > n)
+                continue;
+            // 試行：選択を行い、状態を更新
+            backtrack(choices, state + choice, n, res);
+            // 撤回
+        }
+    }
+
+    /* 階段登り：バックトラッキング */
+    public static int climbingStairsBacktrack(int n) {
+        List<Integer> choices = Arrays.asList(1, 2); // 1段または2段登ることを選択可能
+        int state = 0; // 0段目から登り始める
+        List<Integer> res = new ArrayList<>();
+        res.add(0); // res[0] を使用して解の数を記録
+        backtrack(choices, state, n, res);
+        return res.get(0);
+    }
+
+    public static void main(String[] args) {
+        int n = 9;
+
+        int res = climbingStairsBacktrack(n);
+        System.out.println(String.format("%d段の階段を登る解は%d通りです", n, res));
+    }
+}