HDU 4704 Sum （费马定理+快速幂）

Sum

Time Limit: 2000/1000 MS (Java/Others)    Memory Limit: 131072/131072 K (Java/Others)
Total Submission(s): 647    Accepted Submission(s): 320

Problem DescriptionSample InputSample OutputSourceimport java.io.*;import java.util.*;import java.math.*;public class Main {BigInteger n;String s="";BigInteger one=BigInteger.valueOf(1);BigInteger Mod=BigInteger.valueOf((long)(1e9+7));BigInteger Mod1=BigInteger.valueOf((long)(1e9+6));public static void main(String[] args) {new Main().work();}void work(){Scanner sc=new Scanner(new BufferedInputStream(System.in));while(sc.hasNext()){s=sc.next();n=BigInteger.valueOf(0);for(int i=0;i<s.length();i++){n=(n.multiply(BigInteger.valueOf(10)).add(BigInteger.valueOf(s.charAt(i)-'0'))).mod(Mod1);}long num=n.longValue()-1;System.out.println(pow(BigInteger.valueOf(2),num).mod(Mod)); }}BigInteger pow(BigInteger a,long b){BigInteger sum=BigInteger.ONE;while(b!=00){if((b&1)!=0){sum=sum.multiply(a).mod(Mod);}a=a.multiply(a).mod(Mod);b>>=1;}return sum;}}