Ural 1095 Nikifor 3 数论
来源：http://acm.timus.ru/problem.aspx?space=1&num=1095
题意：给你一个数，其中包含数字1 2 3 4，让你对这个数的数字重新排列，使其目的数能被7整除。
思路：经过计算发现，1234有24种全排列，对7取余，其中包含了0，1，2，3，4，5，6这7种情况。所以，只需要计算除去1 2 3 4以外的数对7取余的结果，然后让后面的1234对其补余即可。需要注意一种特殊情况如1001234，在去1234时，把第一个1去掉了，这样的后果是求出的去掉1234后的数为1.为防止这种情况，可以最后补0。本来以为用到大数，所以用java写的。其实用C++完全可以搞定。。
代码：
import java.util.*;import java.math.BigInteger;public class Main {public static void main(String[] args){ Scanner cin = new Scanner(System.in); int numcase; numcase = cin.nextInt(); for(int j = 1; j <= numcase; ++j){ BigInteger n; int flag1 = 0,flag2 = 0,flag3 = 0,flag4 =0; n = cin.nextBigInteger(); String ss = n.toString(); BigInteger x = new BigInteger("0"); BigInteger x1 = new BigInteger("1"); BigInteger x2 = new BigInteger("2"); BigInteger x3 = new BigInteger("3"); BigInteger x4 = new BigInteger("4"); BigInteger x5 = new BigInteger("5"); BigInteger x6 = new BigInteger("6"); BigInteger sum = x ; char ch[] = ss.toCharArray(); int cntzero = 0; for(int i = 0;i < ss.length(); ++i){ if(ch[i] == '1' && flag1 == 0){ flag1 = 1; continue; } else if(ch[i] == '2' && flag2 == 0){ flag2 = 1; continue; } else if(ch[i] == '3' && flag3 == 0){ flag3 = 1; continue; } else if(ch[i] == '4' && flag4 == 0){ flag4 = 1; continue; } else if(ch[i] == '0'){ cntzero++; continue; } int y = ch[i] - '0'; BigInteger z = new BigInteger(""+y); BigInteger zz = new BigInteger("10"); sum = sum.multiply(zz); sum = sum.add(z); } BigInteger p = new BigInteger("10000"); sum = sum.multiply(p); ss = sum.toString(); // System.out.println(ss); BigInteger q = new BigInteger("7"); BigInteger mm = sum.mod(q); mm = q.subtract(mm); ss = mm.toString(); // System.out.println(ss); BigInteger ans; if(mm.compareTo(q) == 0){ ans = new BigInteger("3241"); sum = sum.add(ans); ss = sum.toString(); System.out.print(ss); } else if(mm.compareTo(x1) == 0){ ans = new BigInteger("1324"); sum = sum.add(ans); ss = sum.toString(); System.out.print(ss); } else if(mm.compareTo(x2) == 0){ ans = new BigInteger("1234"); sum = sum.add(ans); ss = sum.toString(); System.out.print(ss); } else if(mm.compareTo(x3) == 0){ ans = new BigInteger("2341"); sum = sum.add(ans); ss = sum.toString(); System.out.print(ss); } else if(mm.compareTo(x4) == 0){ ans = new BigInteger("1243"); sum = sum.add(ans); ss = sum.toString(); System.out.print(ss); } else if(mm.compareTo(x5) == 0){ ans = new BigInteger("1342"); sum = sum.add(ans); ss = sum.toString(); System.out.print(ss); } else if(mm.compareTo(x6) == 0){ ans = new BigInteger("2134"); sum = sum.add(ans); ss = sum.toString(); System.out.print(ss); } for(int k = 0; k < cntzero; ++k) System.out.print(0); System.out.println(); }}}