好久沒用遞迴了,趕快找個簡單的題目複習一下,不然都要忘光光了,熟悉一下之前的Feel ~
順便練習一下簡單工廠模式,首先設計介面ICompute.cs
:
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30
|
interface ICompute { /// <summary> /// 1 + ... + N = ? /// </summary> /// <param name="n"></param> /// <returns>Answer</returns> Int64 Iterative(Int64 n); /// <summary> /// 1 - 2 + 3 ... + N = ? /// </summary> /// <param name="n"></param> /// <returns>Answer</returns> Int64 AdvancedIterative(Int64 n); /// <summary> /// 1 x 2 x ... x N = ? /// </summary> /// <param name="n"></param> /// <returns>Answer</returns> Int64 Factorial(Int64 n); /// <summary> /// Fn = Fn-1 + Fn-2 /// </summary> /// <param name="n"></param> /// <returns>Answer</returns> Int64 Fibonacci(Int64 n); } |
接著建立兩個類別Recursive.cs
與ForLoop.cs
並繼承ICompute.cs
實作其方法:
- Recursive.cs
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
|
public class Recursive : ICompute { public Int64 Iterative(Int64 n) { if (n == 1) { return n; } else { return n + Iterative(n - 1); } } public Int64 AdvancedIterative(Int64 n) { if (n == 1) { return n; } else { return n % 2 == 0 ? -n + AdvancedIterative(n - 1) : n + AdvancedIterative(n - 1); } } public Int64 Factorial(Int64 n) { if (n == 1) { return n; } else { return n * Factorial(n - 1); } } public Int64 Fibonacci(Int64 n) { if (n < 3) { return 1; } else { return Fibonacci(n - 1) + Fibonacci(n - 2); } } } |
- ForLoop.cs
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68
|
public class ForLoop : ICompute { public Int64 Iterative(Int64 n) { int ans = 0; for (int i = 1; i <= n; i++) { ans += i; } return ans; } public Int64 AdvancedIterative(Int64 n) { int ans = 0; for (int i = 1; i <= n; i++) { if (i % 2 == 0) { ans -= i; } else { ans += i; } } return ans; } public Int64 Factorial(Int64 n) { int ans = 1; for (int i = 1; i <= n; i++) { ans *= i; } return ans; } public Int64 Fibonacci(Int64 n) { int ans = 0; int[] arr = new int[2] { 1, 1 }; for (int i = 1; i <= n; i++) { if (i < 3) { ans = 1; } else { ans = arr[0] + arr[1]; arr[0] = arr[1]; arr[1] = ans; } } return ans; } } |
接著在Program.cs
裡面寫一個Run的方法來呼叫剛剛寫好的兩個類別:
|
static void Run(int n, ICompute compute) { Console.WriteLine("1 + ... + N = {1}", n, compute.Iterative(n)); Console.WriteLine("1 - 2 + 3 ... + N = {1}", n, compute.AdvancedIterative(n)); Console.WriteLine("N! = {1}", n, compute.Factorial(n)); Console.WriteLine("Fn = Fn-1 + Fn-2, n = {0}, Ans = {1}", n, compute.Fibonacci(n)); } |
這樣就完成囉 !!
原始碼:https://github.com/shuangrain/RecursiveEample