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_heap/top_k.java

@@ -0,0 +1,40 @@
+/**
+ * File: top_k.java
+ * Created Time: 2023-06-12
+ * Author: krahets (krahets@163.com)
+ */
+
+package chapter_heap;
+
+import utils.*;
+import java.util.*;
+
+public class top_k {
+    /* ヒープを使用して配列内の最大 k 個の要素を検索 */
+    static Queue<Integer> topKHeap(int[] nums, int k) {
+        // 最小ヒープを初期化
+        Queue<Integer> heap = new PriorityQueue<Integer>();
+        // 配列の最初の k 個の要素をヒープに入力
+        for (int i = 0; i < k; i++) {
+            heap.offer(nums[i]);
+        }
+        // k+1 番目の要素から、ヒープの長さを k に保つ
+        for (int i = k; i < nums.length; i++) {
+            // 現在の要素がヒープの先頭要素より大きい場合、ヒープの先頭要素を削除し、現在の要素をヒープに入力
+            if (nums[i] > heap.peek()) {
+                heap.poll();
+                heap.offer(nums[i]);
+            }
+        }
+        return heap;
+    }
+
+    public static void main(String[] args) {
+        int[] nums = { 1, 7, 6, 3, 2 };
+        int k = 3;
+
+        Queue<Integer> res = topKHeap(nums, k);
+        System.out.println("最大 " + k + " 個の要素は");
+        PrintUtil.printHeap(res);
+    }
+}