Add the section of iteration and recursion. (#693)

codes/python/chapter_computational_complexity/iteration.py

@@ -0,0 +1,65 @@
+"""
+File: iteration.py
+Created Time: 2023-08-24
+Author: Krahets (krahets@163.com)
+"""
+
+
+def for_loop(n: int) -> int:
+    """for 循环"""
+    res = 0
+    # 循环求和 1, 2, ..., n-1, n
+    for i in range(1, n + 1):
+        res += i
+    return res
+
+
+def while_loop(n: int) -> int:
+    """while 循环"""
+    res = 0
+    i = 1  # 初始化条件变量
+    # 循环求和 1, 2, ..., n-1, n
+    while i <= n:
+        res += i
+        i += 1  # 更新条件变量
+    return res
+
+
+def while_loop_ii(n: int) -> int:
+    """while 循环（两次更新）"""
+    res = 0
+    i = 1  # 初始化条件变量
+    # 循环求和 1, 2, 4, 5...
+    while i <= n:
+        res += i
+        i += 1  # 更新条件变量
+        res += i
+        i *= 2  # 更新条件变量
+    return res
+
+
+def nested_for_loop(n: int) -> str:
+    """双层 for 循环"""
+    res = ""
+    # 循环 i = 1, 2, ..., n-1, n
+    for i in range(1, n + 1):
+        # 循环 j = 1, 2, ..., n-1, n
+        for j in range(1, n + 1):
+            res += f"({i}, {j}), "
+    return res
+
+
+"""Driver Code"""
+if __name__ == "__main__":
+    n = 5
+    res = for_loop(n)
+    print(f"\nfor 循环的求和结果 res = {res}")
+
+    res = while_loop(n)
+    print(f"\nwhile 循环的求和结果 res = {res}")
+
+    res = while_loop_ii(n)
+    print(f"\nwhile 循环（两次更新）求和结果 res = {res}")
+
+    res = nested_for_loop(n)
+    print(f"\n双层 for 循环的遍历结果 {res}")