c++递归算法经典实例（排列问题c++递归实现）

方法一：递归算法

1 2 3 4 5 6 7 8 9 10 11 12 13 14 /// <summary> /// 一列数的规则如下: 1、1、2、3、5、8、13、21、34求第30位数是多少，用递归算法实现。(C#语言) /// </summary> /// <param name="pos"></param> /// <returns></returns> public int GetNumberAtPos(int pos) { if(pos==0||pos==1) { return 1; } int res = GetNumberAtPos(pos - 1) + GetNumberAtPos(pos - 2); return res; }

方法二：不用递归

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 69 70 71 72 73 74 75 76 using System; using System.Collections; using System.Collections.Generic; using System.Text; namespace Test { public class Class1 { private ArrayList list = new ArrayList(); public Class1() { } public Class1(int num) : base() { int i; for (i = 1; i <= num; i++) { list.Add(Calculation(i)); } } private int Calculation(int num) { if (num == 1 || num == 2) return 1; else return Convert.ToInt32(list[num - 2]) + Convert.ToInt32(list[num - 3]); } public int Calculation() { return Convert.ToInt32(list[list.Count - 1]); } } public class test { public static void Main() { int j; int num; for (j = 1; j < 100; j++) { Console.WriteLine("你要计算第多少位:"); string readstr; readstr = Console.ReadLine(); if (!string.IsNullOrEmpty(readstr)) { if (int.TryParse(readstr, out num)) { if (num < 1) continue; else { Class1 c1 = new Class1(num); Console.WriteLine(c1.Calculation()); } } else { continue; } } else { break; } } } } }

方法三：用循环实现

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 public long getNumber(int pos) { long one = 1; long two = 1; if (pos == 0 || pos == 1) { return 1; } int i = 3; long sum = 1; while (i <= pos) { sum = one + two; one = two; two = sum; i++; } return sum; }