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/cpp/chapter_heap/top_k.cpp

@@ -0,0 +1,38 @@
+/**
+ * File: top_k.cpp
+ * Created Time: 2023-06-12
+ * Author: krahets (krahets@163.com)
+ */
+
+#include "../utils/common.hpp"
+
+/* ヒープを使用して配列内の最大k個の要素を見つける */
+priority_queue<int, vector<int>, greater<int>> topKHeap(vector<int> &nums, int k) {
+    // 最小ヒープを初期化
+    priority_queue<int, vector<int>, greater<int>> heap;
+    // 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.push(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.size(); 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.top()) {
+            heap.pop();
+            heap.push(nums[i]);
+        }
+    }
+    return heap;
+}
+
+// ドライバーコード
+int main() {
+    vector<int> nums = {1, 7, 6, 3, 2};
+    int k = 3;
+
+    priority_queue<int, vector<int>, greater<int>> res = topKHeap(nums, k);
+    cout << "最大 " << k << " 個の要素は:";
+    printHeap(res);
+
+    return 0;
+}