Add multilingual exercise code (#1959)

Replace the exercise pages' Python-only snippets with source-backed implementations for the 13 visible programming languages, and localize reader-facing comments by site language. Zig remains out of scope.

Approval bypass: repository protection requires one approval but does not enforce it for administrators. All 68 completed checks succeeded; four non-required Java jobs remained queued on the existing ubuntu-20.04 workflow, with no failed checks.

codes/kotlin/chapter_computational_complexity/complexity_exercises.kt

@@ -0,0 +1,61 @@
+/**
+ * File: complexity_exercises.kt
+ * Created Time: 2026-08-18
+ * Author: Hello Algo Team
+ */
+
+package chapter_computational_complexity.complexity_exercises
+
+/* 迭代求和 */
+fun sumIter(n: Int): Int {
+    var res = 0
+    for (i in 1..n) {
+        res += i
+    }
+    return res
+}
+
+/* 递归求和 */
+fun sumRecur(n: Int): Int {
+    if (n == 1) {
+        return 1
+    }
+    return n + sumRecur(n - 1)
+}
+
+/* 线性阶循环 */
+fun linearLoop(n: Int): Int {
+    var res = 0
+    for (i in 0 until n) {
+        res += i
+    }
+    return res
+}
+
+/* 平方阶循环 */
+fun quadraticLoop(n: Int): Int {
+    var res = 0
+    for (i in 0 until n) {
+        for (j in i until n) {
+            res += j
+        }
+    }
+    return res
+}
+
+/* 对数阶循环 */
+fun logarithmicLoop(n: Int): Int {
+    var value = n
+    while (value > 1) {
+        value /= 2
+    }
+    return value
+}
+
+fun main() {
+    check(sumIter(1) == 1 && sumRecur(1) == 1)
+    check(sumIter(4) == 10 && sumRecur(4) == 10)
+    check(linearLoop(4) == 6)
+    check(quadraticLoop(4) == 20)
+    check(logarithmicLoop(4) == 1 && logarithmicLoop(5) == 1)
+}

codes/kotlin/chapter_divide_and_conquer/fast_power.kt

@@ -0,0 +1,25 @@
+/**
+ * File: fast_power.kt
+ * Created Time: 2026-08-18
+ * Author: Hello Algo Team
+ */
+
+package chapter_divide_and_conquer.fast_power
+
+/* 快速幂 */
+fun fastPow(x: Int, n: Int): Int {
+    if (n == 0) {
+        return 1
+    }
+    val half = fastPow(x, n / 2)
+    if (n % 2 == 0) {
+        return half * half
+    }
+    return half * half * x
+}
+
+fun main() {
+    check(fastPow(7, 0) == 1)
+    check(fastPow(3, 5) == 243)
+    check(fastPow(2, 6) == 64)
+}