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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codes/swift/chapter_computational_complexity/complexity_exercises.swift

@@ -0,0 +1,62 @@
+/**
+ File: complexity_exercises.swift
+ Created Time: 2026-08-18
+ Author: Hello Algo Team
+ */
+
+/* 迭代求和 */
+func sumIter(n: Int) -> Int {
+    var res = 0
+    for i in 1 ... n {
+        res += i
+    }
+    return res
+}
+
+/* 递归求和 */
+func sumRecur(n: Int) -> Int {
+    if n == 1 {
+        return 1
+    }
+    return n + sumRecur(n: n - 1)
+}
+
+/* 线性阶循环 */
+func linearLoop(n: Int) -> Int {
+    var res = 0
+    for i in 0 ..< n {
+        res += i
+    }
+    return res
+}
+
+/* 平方阶循环 */
+func quadraticLoop(n: Int) -> Int {
+    var res = 0
+    for i in 0 ..< n {
+        for j in i ..< n {
+            res += j
+        }
+    }
+    return res
+}
+
+/* 对数阶循环 */
+func logarithmicLoop(n: Int) -> Int {
+    var n = n
+    while n > 1 {
+        n /= 2
+    }
+    return n
+}
+
+@main
+enum ComplexityExercises {
+    static func main() {
+        assert(sumIter(n: 1) == 1 && sumRecur(n: 1) == 1)
+        assert(sumIter(n: 4) == 10 && sumRecur(n: 4) == 10)
+        assert(linearLoop(n: 4) == 6)
+        assert(quadraticLoop(n: 4) == 20)
+        assert(logarithmicLoop(n: 4) == 1 && logarithmicLoop(n: 5) == 1)
+    }
+}