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.

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en/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
+
+/* Iterative summation */
+fun sumIter(n: Int): Int {
+    var res = 0
+    for (i in 1..n) {
+        res += i
+    }
+    return res
+}
+
+/* Recursive summation */
+fun sumRecur(n: Int): Int {
+    if (n == 1) {
+        return 1
+    }
+    return n + sumRecur(n - 1)
+}
+
+/* Linear loop */
+fun linearLoop(n: Int): Int {
+    var res = 0
+    for (i in 0 until n) {
+        res += i
+    }
+    return res
+}
+
+/* Quadratic loop */
+fun quadraticLoop(n: Int): Int {
+    var res = 0
+    for (i in 0 until n) {
+        for (j in i until n) {
+            res += j
+        }
+    }
+    return res
+}
+
+/* Logarithmic loop */
+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)
+}