1515：打印1到最大的N位数 @jobdu

题目1515：打印1到最大的N位数

考察的就是大数据输入。

这种求全部组合的题目，一概可以用DFS来做。虽然本题Java中有自带BigInteger类，但还是按照出题人的意思来做吧。

import java.io.BufferedInputStream;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.util.Scanner;


public class S12 {

	public static void main(String[] args) throws FileNotFoundException {
		BufferedInputStream in = new BufferedInputStream(new FileInputStream("in.in"));
		System.setIn(in);
		Scanner cin = new Scanner(System.in);
		
		while (cin.hasNextInt()) {
			int n = cin.nextInt();
			print1ToMaxOfNDigits(n);
		}
	}

	private static void print1ToMaxOfNDigits(int n) {
		if(n <= 0){
			return;
		}
		
		char[] number = new char[n];
		rec(number, n, 0);
	}
	
	private static void rec(char[] number, int length, int curDep){
		if(curDep == length){
			printNumber(number);
			return;
		}
		
		for(int i=0; i<10; i++){
			number[curDep] = (char) (i+'0');
			rec(number, length, curDep+1);
		}
	}
	
	private static void printNumber(char[] number){
		boolean startingZero = true;
		for(int i=0; i<number.length; i++){
			if(number[i] != '0'){		// 过滤掉前导零
				startingZero = false;
			}
			if(!startingZero){
				System.out.print(number[i]);
			}
		}
		if(!startingZero){
			System.out.println();
		}
		
	}
}