完数

题目：http://www.51nod.com/onlineJudge/questionCode.html#!problemId=1114

题意：给定一个数n，求满足条件大于等于n的最小的完数。

分析：我们先把前13个完数存进数组，然后比较即可。因为第13个完数的位数已经大于100位了，所以再大的就用不着了。

再利用Java的BigInteger进行比较很方便。

import java.io.*;
import java.util.*;
import java.math.BigInteger;
 
public class Main{
		public static void main(String[] args){
				Scanner cin = new Scanner(System.in);
				String[] str = {
						"6",
						"28",
						"496",
						"8128",
						"33550336",
						"8589869056",
						"137438691328",
						"2305843008139952128",
						"2658455991569831744654692615953842176",
						"191561942608236107294793378084303638130997321548169216",
						"13164036458569648337239753460458722910223472318386943117783728128",
						"14474011154664524427946373126085988481573677491474835889066354349131199152128",
						"23562723457267347065789548996709904988477547858392600710143027597506337283178622239730365539602600561360255566462503270175052892578043215543382498428777152427010394496918664028644534128033831439790236838624033171435922356643219703101720713163527487298747400647801939587165936401087419375649057918549492160555646976"
						};
				BigInteger data[] = new BigInteger[15];
				for(int i=0;i<13;i++)
					data[i] = new BigInteger(str[i]);
				while(cin.hasNextBigInteger()){
						BigInteger n = cin.nextBigInteger();
						for(int i=0;i<13;i++){
								if(data[i].compareTo(n) == 0 || data[i].compareTo(n) == 1){
										System.out.println(data[i]);
										break;
								}
						}
				}
		}
}