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/python/chapter_computational_complexity/complexity_exercises.py

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+"""
+File: complexity_exercises.py
+Created Time: 2026-08-18
+Author: Hello Algo Team
+"""
+
+
+def sum_iter(n: int) -> int:
+    """Iterative summation"""
+    res = 0
+    for i in range(1, n + 1):
+        res += i
+    return res
+
+
+def sum_recur(n: int) -> int:
+    """Recursive summation"""
+    if n == 1:
+        return 1
+    return n + sum_recur(n - 1)
+
+
+def linear_loop(n: int) -> int:
+    """Linear loop"""
+    res = 0
+    for i in range(n):
+        res += i
+    return res
+
+
+def quadratic_loop(n: int) -> int:
+    """Quadratic loop"""
+    res = 0
+    for i in range(n):
+        for j in range(i, n):
+            res += j
+    return res
+
+
+def logarithmic_loop(n: int) -> int:
+    """Logarithmic loop"""
+    while n > 1:
+        n //= 2
+    return n
+
+
+if __name__ == "__main__":
+    assert sum_iter(1) == sum_recur(1) == 1
+    assert sum_iter(4) == sum_recur(4) == 10
+    assert linear_loop(4) == 6
+    assert quadratic_loop(4) == 20
+    assert logarithmic_loop(4) == logarithmic_loop(5) == 1

en/codes/python/chapter_divide_and_conquer/fast_power.py

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+"""
+File: fast_power.py
+Created Time: 2026-08-18
+Author: Hello Algo Team
+"""
+
+
+def fast_pow(x: int, n: int) -> int:
+    """Exponentiation by squaring"""
+    if n == 0:
+        return 1
+    half = fast_pow(x, n // 2)
+    if n % 2 == 0:
+        return half * half
+    return half * half * x
+
+
+if __name__ == "__main__":
+    assert fast_pow(7, 0) == 1
+    assert fast_pow(3, 5) == 243
+    assert fast_pow(2, 6) == 64