Re-translate the Japanese version (#1871)

* Retranslate Japanese docs with GPT-5.4

* Retranslate Japanese code with GPT-5.4

ja/codes/csharp/chapter_searching/two_sum.cs

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+/**
+ * File: two_sum.cs
+ * Created Time: 2022-12-23
+ * Author: haptear (haptear@hotmail.com)
+ */
+
+namespace hello_algo.chapter_searching;
+
+public class two_sum {
+    /* 方法 1：総当たり列挙 */
+    int[] TwoSumBruteForce(int[] nums, int target) {
+        int size = nums.Length;
+        // 2重ループのため、時間計算量は O(n^2)
+        for (int i = 0; i < size - 1; i++) {
+            for (int j = i + 1; j < size; j++) {
+                if (nums[i] + nums[j] == target)
+                    return [i, j];
+            }
+        }
+        return [];
+    }
+
+    /* 方法 2：補助ハッシュテーブル */
+    int[] TwoSumHashTable(int[] nums, int target) {
+        int size = nums.Length;
+        // 補助ハッシュテーブルを使用し、空間計算量は O(n)
+        Dictionary<int, int> dic = [];
+        // 単一ループで、時間計算量は O(n)
+        for (int i = 0; i < size; i++) {
+            if (dic.ContainsKey(target - nums[i])) {
+                return [dic[target - nums[i]], i];
+            }
+            dic.Add(nums[i], i);
+        }
+        return [];
+    }
+
+    [Test]
+    public void Test() {
+        // ======= Test Case =======
+        int[] nums = [2, 7, 11, 15];
+        int target = 13;
+
+        // ====== Driver Code ======
+        // 方法 1
+        int[] res = TwoSumBruteForce(nums, target);
+        Console.WriteLine("方法1 res = " + string.Join(",", res));
+        // 方法 2
+        res = TwoSumHashTable(nums, target);
+        Console.WriteLine("方法2 res = " + string.Join(",", res));
+    }
+}