递归大总结之打印大数1-n

递归

#include<iostream>
using namespace std;
void PrintfNumber(char num[])
{
  bool isBegin0 = true;
  int nlength = strlen(num);
  for (int i = 0; i < nlength; ++i)
  {
    if (isBegin0&&num[i] != '0')
    {
      isBegin0 = false;
    }
    if (!isBegin0)
    {
      cout << num[i];
    }
  }
}
void PrintToMaxDigits2(char *num, int length, int index)
{
  if (index == length - 1)
  {
    PrintfNumber(num);
    return;
  }
  for (int i = 0; i < 10; i++)
  {
    num[index + 1] = i + '0';
    PrintToMaxDigits2(num, length, index + 1);//
  }
}
void PrintToMaxofDigits(int n)
{
  if (n <= 0)
  {
    return;
  }
  char *num = new char[n + 1];
  num[n] = '\0';
  for (int i = 0; i < 10; i++)
  {
    num[0] = i + '0';
    PrintToMaxDigits2(num, n, 0);
  }
}
int main()
{
  int n;
  cin >> n;
  PrintToMaxofDigits(n);
  system("pause");
}

详解

//以n等于3为例
void PrintToMaxDigits2(char *num, int length, int index)
{
  if (index == length - 1)
  {
    PrintfNumber(num);
    return;
  }
  for (int i = 0; i < 10; i++)
  {
    num[index + 1] = i + '0';
    PrintToMaxDigits2(num, length, index + 1);//
    /*
    index=1；
    for (int i = 0; i < 10; i++)
    {
      num[index + 1] = i + '0';
      PrintToMaxDigits2(num, 3, index + 1);
          if (index == length - 1)
          {
            //打印了1-9，这时num[1]还是1，当num[1]是2时再打印1-9
            PrintfNumber(num);
            
            return;
          }
    
    }

    */
  }
}