Question:
http://www.lintcode.com/en/problem/print-numbers-by-recursion/
Print numbers from 1 to the largest number with N digits by recursion.

Answer:

#include <iostream>
using namespace std;

void PrintNumber(char* number, int len) {
  bool isb0 = true;
  for (int i = 0; i < len; i++) {
    if (isb0 && number[i] != '0')
      isb0 = false;
    if (!isb0)
      cout << number[i];
  }
  cout << " ";
}

void Print1ToMaxRecurse(char* number, int length, int index) {
  if (index == (length - 1)) {
    PrintNumber(number, length);
    return;
  }
  for (int i = 0; i < 10; i++) {
    number[index+1] = i+'0';
    Print1ToMaxRecurse(number, length, index+1);
  }
}

void Print1ToMax(int n) {
  if (n <= 0)
    return;
  char *number = new char[n+1];
  number[n] = '\0';
  for (int i = 0; i < 10; i++) {
    number[0]=i+'0';
    Print1ToMaxRecurse(number, n, 0);
  }
  cout << endl;
}

int main() {
  int n;
  cin >> n;
  Print1ToMax(n);
  return 0;
}