面試題12：打印1到最大的n位數-大數問題-遞歸實現多層循環

#include <iostream>
#include <stack>
#include <queue>
#include <algorithm>
#include <string.h>
#include <cstdio>
#include <stdlib.h>

using namespace std;


void printToMaxNdigits( int n )
{
	if( n < 1 )
	{
		cout << "printToMaxNdigits func: err -1, n < 1 " << endl;	
		return;
	}

	char *p = new char[ n + 2 ];

	if( NULL == p )
	{
		cout << "printToMaxNdigits func: err -1, NULL == p " << endl;	
		return;
	}


	memset( p, '\0', n + 2 );

	strcpy( p, "1" );
	int curLen = strlen(p);

	while( curLen <= n )
	{
		cout << p << endl;
		int up = 0;

		int len = strlen(p);
		char tmp = '0';

		for( int i = len - 1; i >= 0; i-- )
		{
			if( i == len - 1 )
			{
				tmp = p[i] + 1;
			}
			else
			{
				tmp = p[i] + up;
			}
			
	
			if( tmp > '9' )
			{
				up = 1;
				p[i] = '0';
			}
			else
			{
				up = 0;
				p[i] = tmp;
			}
		}	

		if( 1 == up )
		{
			for( int j = len - 1; j >= 0; j-- )
			{
				p[ j + 1 ] = p[j];
			}

			p[0] = '1';
		}	

		curLen = strlen(p);

	}

	delete []p;
	p = NULL;
	return;
}

// 遞歸解決
void printNumber( char *p )
{
	int len = strlen(p);
	bool begin = false;

	for( int i = 0; i < len; i++ )
	{
		if( !begin && p[i] != '0' )
		{
			begin = true;
		}
	
		if( begin )
		{
			cout << p[i];
		}
	}

	if( begin )
	{
		cout << endl;
	}
	
	return;
}


void print1ToMaxOfNDigitsRecursively( char *p, int n, int index )
{
	if( index == n - 1 )
	{
		printNumber(p);
		return;
	}	

	for( int i = 0; i < 10; i++ )
	{
		p[ index + 1 ] = '0' + i;
		print1ToMaxOfNDigitsRecursively( p, n, index + 1 );
	}

	return;
}


void printToNDigits( int n )
{
	if( n < 1 )
	{
		cout << "printToNDigits func: err -1, n < 1 " << endl;
		return;
	}

	char *p = new char[ n + 2 ];
	
	if( NULL == p )
	{
		cout << "printToNDigits func: err -1, NULL == p " << endl;	
		return;
	}

	memset( p, '0', n + 2 );
	p[n] = '\0';

	for( int i = 0; i < 10; i++ )
	{
		p[0] = '0' + i;
		print1ToMaxOfNDigitsRecursively( p, n, 0 );
	}

	return;
}

// n表示幾層循環，cur表示當前處於第幾層，result表示當前結果
void myrecursion( int n, int cur, int result )
{
	if( cur == n )
	{
		cout << result << endl;
		return;		
	}

	for( int i = 1; i <= 10; i++ )
	{
		myrecursion( n, cur + 1, result + i );
	}

	return;
}



int main()
{
	int ret = 0;
	myrecursion( 2, 0, 0 );

//	printToMaxNdigits(8);
	//printToNDigits(5);
	return ret;
}