題意：給你一個數，其中包含數字1 2 3 4，讓你對這個數的數字重新排列，使其目的數能被7整除。
思路：經過計算發現，1234有24種全排列，對7取余，其中包含了0，1，2，3，4，5，6這7種情況。所以，只需要計算除去1 2 3 4以外的數對7取余的結果，然後讓後面的1234對其補余即可。需要注意一種特殊情況如1001234，在去1234時，把第一個1去掉了，這樣的後果是求出的去掉1234後的數為1.為防止這種情況，可以最後補0。本來以為用到大數，所以用java寫的。其實用C++完全可以搞定。。
代碼：
[cpp] www.2cto.com
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();
}
}
}
作者：wmn_wmn
